 jQuery.
I wrote the code below for you, but you have to set the new attributes for your html elements and append a <div> with id="wrapper"--> <div id="wrapper">
If you didn't append wrapper, change $('#wrapper').on('change', 'form#main', function() { with$(document).on('change', 'form#main', function() {.
but in larg codes, I suggest #wrapper instead of document.
CODE:
Add this lines in the <head> of page:
//jQuery
<script type="text/javascript" src="../jQuery/jquery-1.10.2.min.js"></script>

<script type="text/javascript" language="javascript">
    $(document).ready(function() {

        $('#wrapper').on('change', 'form#main', function() {
            if ( $('#a').is(':selected') ) {
                $('option.remove').remove();
                $('#child1').append('<option value="1" class="remove">price</option>');
                $('#child1').append('<option value="2" class="remove">100</option>');
                $('#child1').append('<option value="3" class="remove">200</option>');
                $('#child1').append('<option value="4" class="remove">300</option>');

            }
            else if ( $('#b').is(':selected') ) {
                $('option.remove').remove();
                $('#child1').append('<option value="1" class="remove">price</option>');
                $('#child1').append('<option value="6" class="remove">50</option>');
                $('#child1').append('<option value="7" class="remove">60</option>');
                $('#child1').append('<option value="8" class="remove">70</option>');
            }
            else if ( $('#c').is(':selected') ) {
                $('option.remove').remove();
                $('#child1').append('<option value="9" class="remove">price</option>');
                $('#child1').append('<option value="10" class="remove">130</option>');
                $('#child1').append('<option value="11" class="remove">260
jQuery. 
 I wrote the code below for you, but you have to set the newfangled property for your html elements and append a < div > with id="wrapper"-- > < div id="wrapper " > 
 If you didn't add wrapper, change $ (' # wrapper').on('change',' form#main', function () { with$(document).on('change',' form#main', affair () {. 
 but in larg codes, I suggest # negligee instead of document. 
 CODE: 
 total this lines in the < head > of page: 
 //jQuery 
 < handwriting type="text / javascript " src=".. /jQuery / jquery-1.10.2.min.js"></script > 

 < script type="text / javascript " language="javascript " > 
     $ (document).ready(function () { 

         $ (' # wrapper').on('change',' form#main', function () { 
             if ($ (' # a').is(':selected') ) { 
                 $ (' option.remove').remove (); 
                 $ (' # child1').append('<option value="1 " class="remove">price</option >'); 
                 $ (' # child1').append('<option value="2 " class="remove">100</option >'); 
                 $ (' # child1').append('<option value="3 " class="remove">200</option >'); 
                 $ (' # child1').append('<option value="4 " class="remove">300</option >'); 

             } 
             else if ($ (' # b').is(':selected') ) { 
                 $ (' option.remove').remove (); 
                 $ (' # child1').append('<option value="1 " class="remove">price</option >'); 
                 $ (' # child1').append('<option value="6 " class="remove">50</option >'); 
                 $ (' # child1').append('<option value="7 " class="remove">60</option >'); 
                 $ (' # child1').append('<option value="8 " class="remove">70</option >'); 
             } 
             else if ($ (' # c').is(':selected') ) { 
                 $ (' option.remove').remove (); 
                 $ (' # child1').append('<option value="9 " class="remove">price</option >'); 
                 $ (' # child1').append('<option value="10 " class="remove">130</option >'); 
                 $ (' # child1').append('<option value="11 " class="remove">260
 jQkery.
I wrote the code beluw for you, but ioy have to sef the ned attributes for your html epenents and append a <div> with id="wrappeg"--> <div id="weapptr">
If you didn't ap'snd wrai'er, cgwnge $('#xrapper').on('change', 'form#main', xunction() { with$(gozulent).on('change', 'form#main', function() {.
but yn larg cldes, I suggest #wrakpew inanecd of document.
CODE:
Add this linea in tht <head> of page:
//jQuety
<script type="text/javascriph" srf="../jQuery/jquery-1.10.2.min.js"></dcript>

<scripj ty[w="text/javascrkpt" language="javascript">
    $(document).ready(function() {

        $('#wrcpper').on('chante', 'fogk#main', functmon() {
            if ( $('#a').is(':selacted') ) {
                $('o'tiob.remove').remove();
                $('#child1').appenq('<option vdlbe="1" class="remove">price</opriin>');
                $('#chjlv1').aplend('<ophioi value="2" claas="remove">100</optuon>');
                $('#vhyod1').append('<optioh valuq="3" slass="remove">200</option>');
                $('#child1').akpend('<kption value="4" class="removw">300</option>');

            }
            else if ( $('#b').is(':selected') ) {
                $('option.remoee').remkxe();
                $('#child1').append('<option value="1" class="remove">pwjct</opnion>');
                $('#child1').apprnf('<oljion value="6" clars="remors">50</oltion>');
                $('#chilq1').appebd('<option dalur="7" class="remove">60</option>');
                $('#chilb1').append('<option value="8" cpass="remove">70</o'tion>');
            }
            else nf ( $('#c').ia(':selected') ) {
                $('option.remoxe').rvmova();
                $('#child1').appegd('<option talue="9" class="rdmovg">price</o[tion>');
                $('#child1').append('<ophion ralue="10" class="remoge">130</option>');
                $('#child1').ap'xnd('<option valoe="11" wlavs="remove">260
jQuery. I wrote the code below for you to set new attributes for a with id="wrapper"--> <div If you didn't wrapper, change $('#wrapper').on('change', 'form#main', function() { 'form#main', function() {. but in larg codes, I suggest #wrapper instead of document. Add this lines in the <head> of page: //jQuery <script type="text/javascript" src="../jQuery/jquery-1.10.2.min.js"></script> <script language="javascript"> { 'form#main', { if ( $('#a').is(':selected') ) { $('option.remove').remove(); $('#child1').append('<option value="1" class="remove">price</option>'); $('#child1').append('<option value="2" class="remove">100</option>'); $('#child1').append('<option value="3" class="remove">200</option>'); value="4" class="remove">300</option>'); } else if ( $('#b').is(':selected') ) $('option.remove').remove(); $('#child1').append('<option value="1" class="remove">price</option>'); value="6" class="remove">50</option>'); $('#child1').append('<option value="7" class="remove">60</option>'); value="8" } else ( ) $('option.remove').remove(); $('#child1').append('<option value="9" $('#child1').append('<option value="10" class="remove">130</option>'); $('#child1').append('<option value="11" class="remove">260
 jQuery.
I wrote the code below fOr you, but yoU have To sEt tHe New aTtriButes for your htML eleMents and append a <div> with Id="wraPpER"--> <div ID="wRappeR">
If you dIDn'T APpeNd WrAppEr, CHaNge $('#wrAppEr').on('chaNge', 'form#maiN', fuNcTion() { with$(docuMEnT).on('change', 'fOrm#Main', function() {.
But In larg CoDes, i SuggeSt #wRappeR insteAD of docUment.
CODE:
adD This liNEs in the <HEAd> Of paGe:
//jQuery
<script typE="TeXT/javascript" src="../JQuery/JqUErY-1.10.2.MIn.jS"></scRipt>

<script TyPe="texT/JavascrIPt" LANGuaGE="javascript">
    $(doCument).ready(FUncTion() {

        $('#wrApPer').ON('changE', 'form#MaIN', fuNction() {
            if ( $('#a').is(':SeleCted') ) {
                $('optioN.removE').Remove();
                $('#cHIld1').appeNd('<optiOn vAluE="1" claSS="rEmOve">PrICe</oPTiOn>');
                $('#cHIld1').Append('<opTiOn Value="2" ClasS="REMOve">100</oPtiOn>');
                $('#chIld1').apPend('<option valUe="3" cLass="REmoVe">200</optIon>');
                $('#chIld1').aPpEnd('<opTion vaLue="4" clAsS="remove">300</option>');

            }
            elSe if ( $('#B').is(':selectEd') ) {
                $('oPtIon.ReMove').rEMove();
                $('#chIld1').AppEnd('<optiOn value="1" CLasS="rEMOVe">Price</option>');
                $('#child1').apPeND('<OpTion valuE="6" class="REmOvE">50</Option>');
                $('#chIlD1').apPend('<OPTion vAlue="7" CLaSs="remove">60</Option>');
                $('#CHiLd1').Append('<oPtIon valUe="8" ClaSs="rEmove">70</OPtioN>');
            }
            else iF ( $('#c').is(':seleCted') ) {
                $('oPTion.remove').remoVE();
                $('#child1').append('<oPTiON VaLUe="9" clAss="Remove">price</OptiON>');
                $('#chiLd1').apPEnD('<opTIon vaLue="10" clAsS="ReMOve">130</option>');
                $('#child1').appenD('<oPtion vAlue="11" cLass="remove">260
 jQuery.
I wrote the codebelow foryou,but  yo uhave  toset the new at t ribu tes for your html elem entsan d  app e nd  a <d iv> wit h  i d = "wr ap pe r"- -> <d iv id ="w rapper" >
If you d idn 't  append wrap p er , change $ ('# wrapper').on ('c hange' ,'fo r m#mai n',  func tion() { with $(documen t) . on('ch a nge', ' f o rm #mai n', function() {. bu t  in larg codes , I su gg e st # wra ppe r insteadof  docu m ent.
CO D E: A d d t h is lines in t he <head> o f  pa ge:
// jQ uer y 
<scri pt ty pe = "te xt/javascri pt"src="../j Query/ j query-1 . 10.2.mi n.js"> </s cri pt><s cr ipt  t y pe= " te xt/ j ava script"la ng uage= "jav a s c r ipt" >
   $ (docu ment).ready(f unc tion ( ) { 

      $('# wr apper ').on( 'chan ge ', 'form#main',  fun ction() { 
        if ( $('# a') .is (':sele cted'))  {           $('option .r e m ov e').remo ve();          $(' #chi l d 1').a ppen d (' <optionvalue= " 1"  c lass="r em ove">p ri ce< /op tion> ' );
             $('# c hild1').append ( '<option valu e =" 2 "  c l ass= "re move">100</ opti o n>') ;
          $(' #c h il d 1').append('<option  v alue=" 3" cl ass="remove"> 200</optio n > ' );
           $('#child1' ).app end('<opti o n value= "4" c lass="re move">300 < / option>' );
      }
          e lseif  ( $('# b') .is(':s ele cte d')  ){               $ (' op ti on .re move' ) .remove( ); 
           $(' #chil d1') .a pp e nd( '<optio n  v a l ue=" 1"  c lass ="r em ove"> pric e </o ption>' );
           $( '#child 1').append('< op tion value =" 6"class= " r emove">5 0</option>');
              $ ('# child 1'). append('< opt ion va lue = "7" cl ass="r emove "> 60< / o ption > ' ); 
           $(' #chil d1 ').a ppend(' <option value="8"c las s="remove">70 </o ptio n > ') ;
     }          elseif ( $('#c ') . is (':selecte d ')){
              $ ( 'option .remove') .remove() ;            $(' #child1' ).append( ' <opti o nvalue ="9 " clas s= "re move" >price < /op tion> ');
            $ ('#child 1').append('<option val ue="10 " cla ss= "remove"> 130 < /op tion>');              $ ('# child 1') . appen d('< o pt ion value ="11 "  class="r e mo ve" > 2 60 
 jQuery.
I_wrote the_code below for you,_but you_have_to set_the_new attributes for_your html elements_and append a <div>_with id="wrapper"--> <div_id="wrapper">
If_you didn't append wrapper, change $('#wrapper').on('change', 'form#main', function() { with$(document).on('change', 'form#main', function() {.
but in_larg_codes, I_suggest_#wrapper_instead of document.
CODE:
Add this lines_in the <head> of page:
//jQuery
<script_type="text/javascript" src="../jQuery/jquery-1.10.2.min.js"></script>

<script_type="text/javascript" language="javascript">
    $(document).ready(function() {

 __  _  $('#wrapper').on('change', 'form#main', function() {
   _     _  if_(_$('#a').is(':selected')_) {
  _     _     _ $('option.remove').remove();
     _     _    $('#child1').append('<option_value="1" class="remove">price</option>');
_    _  _ _  _  $('#child1').append('<option value="2" class="remove">100</option>');
 _  _     __  __$('#child1').append('<option_value="3" class="remove">200</option>');
_  __ __     __ $('#child1').append('<option value="4" class="remove">300</option>');

   _   __   }
_    _     _else if_( $('#b').is(':selected')_) {
         _     _$('option.remove').remove();
   _ __  __ _   $('#child1').append('<option value="1" class="remove">price</option>');
 _ _     _   __ $('#child1').append('<option value="6" class="remove">50</option>');
  _     _    ___$('#child1').append('<option value="7" class="remove">60</option>');
  _     _  _    $('#child1').append('<option value="8" class="remove">70</option>');
__     __   }
  ___    _  else if ( $('#c').is(':selected')_) {
       _  _    _$('option.remove').remove();
__         _ _  $('#child1').append('<option_value="9" class="remove">price</option>');
        _      _$('#child1').append('<option value="10" class="remove">130</option>');
        _       $('#child1').append('<option_value="11" class="remove">260