text: // push a function in 'after click btn-c' queue
  $.queue( 'add', 'afterClickBtnC', function( $playground ){
    
    // only create btn-clear in DOM if it does not exist
    if( $( '#btn-clear' ).length === 0 ){
      
      // remove btn-b, c and clear if the clear btn is clicked
      $( '<div id="btn-clear" class="btn">CLEAR</div>' ).bind( 'click', function(){
        
        $( '#btn-b' ).remove();
        $( '#btn-c' ).remove();
        $( '#btn-clear' ).remove();
      }).appendTo( $playground );
    }
  });