<select name="aa">
<option value="a1">a1</option>
<option value="a2">a2</option>
</select>
<SCRIPT LANGUAGE="JavaScript">
<!--
aa.options[1].selected=true;
//-->
</SCRIPT>
<option value="a1">a1</option>
<option value="a2">a2</option>
</select>
<SCRIPT LANGUAGE="JavaScript">
<!--
aa.options[1].selected=true;
//-->
</SCRIPT>
<option value="a1" selected>a1</option>
<option value="a2">a2</option>
</select>
<SCRIPT LANGUAGE="JavaScript">
<!--
function se(){
aa.options[1].selected=true;
}
//-->
</SCRIPT>
<input type="button" onclick="se()" value="选a2">