title: Do not allow duplicate dropdowns
body: <p>I am guessing this is JS or jQuery but I'm not at all fluent with those (just starting to pick them up after many years of PHP).</p>
  
  <p>I have 3 drop down boxes in a form that are all somewhat identical.  All have a list of the same cites that are pulled from a MySQL database and populated via PHP.  Let's say the cities are:</p>
  
  <ul>
  <li>City 1 </li>
  <li>City 2 </li>
  <li>... </li>
  <li>City 8</li>
  </ul>
  
  <p>The default values for the 3 drop downs will be: </p>
  
  <ul>
  <li>Dropdown 1 is City 1</li>
  <li>Dropdown 2 is N/A</li>
  <li>Dropdown 3 is N/A</li>
  </ul>
  
  <p>Basically I just need to make the drop downs work where a city selected in any of 3 automatically removes it from the other 2 drop downs.  In the end there can be no duplicate entries in the 3 pull down lists.  Also I need it to happen dynamically (onChange event?) so that if they select City 4 in the first list it immediately is removed as an option from the other two drop down lists.</p>
  
  <p>Hopefully this makes sense?  Any help is appreciated!</p>