Can I open a dropdownlist using jQuery

<select id="countries">
<option value="1">Country</option>
</select>

$('#countries').attr('size',6);

$('#countries').attr('size',1);

<select id="countries" size="6">
  <option value="1">Country 1</option>
  <option value="2">Country 2</option>
  <option value="3">Country 3</option>
  <option value="4">Country 4</option>
  <option value="5">Country 5</option>
  <option value="6">Country 6</option>
</select>

<select id="countries" multiple="multiple" size="10">
<option value="1">Country</option>
</select>