怎样将下拉列框的值设置为不可选

Question

document.all["下拉框名称"].disabled = true;

Answer 1

<script language="javascript">
document.all["下拉框名称"].disabled = true;
</script>

Answer 2

<script languge="javascript">
    function disabled_select(){
       the_select.disabled=true;    
    }
</script>
    <select id="disabled_select">
      <option value="11">aa</option>
    </select>
    <input type="button" value="disabled" onclick=" disabled_select()">

Answer 3

能满足否:
<select name="vacation" id="vacation">
<option id="ch1" value="Hong Kong"> Hong Kong</option>
<optgroup label="South Pacific">
 <option id="ch2" label="Australia" value="Australia">Australia</option>
 <option id="ch3" label="Fiji" value="Fiji">Wakaya (Fiji Islands)</option>
 <option id="ch4" value="New Zealand">New Zealand</option>
</optgroup>
<option id="ch5" value="home" selected="selected">Your backyard</option>
</select>