var html = document.getElementById('test1').innerHTML;
var x = 1;
var y = 3;
while (y !== x++)
  document.getElementById('test' + x).innerHTML = html;

<select name="test1" id="test1">
  <option value="1">One</option>
  <option value="2">Two</option>
  <option value="3">Three</option>
</select>
<select name="test2" id="test2"></select>
<select name="test3" id="test3"></select>

var html = $('#test1').html();
var x = 1;
var y = 3;
while (y !== x++)
  $('#test' + x).html(html);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="test1" id="test1">
  <option value="1">One</option>
  <option value="2">Two</option>
  <option value="3">Three</option>
</select>
<select name="test2" id="test2"></select>
<select name="test3" id="test3"></select>