[Sweet]

<form method="post" name="myForm" action="">
  <select onChange="this.form[1].selectedIndex = this.form[2].selectedIndex = this.selectedIndex;">
    <option>Яблоко</option>
    <option>Груша</option>
    <option>Тыква</option>		
  </select><hr />
  <select>
    <option>Яблоко</option>
    <option>Груша</option>
    <option>Тыква</option>		
  </select><br />
  <select>
    <option>Яблоко</option>
    <option>Груша</option>
    <option>Тыква</option>		
  </select>
</form>