Select 设立选中项

<script>
function c_ss(va){
var i,num,op
num=document.form1.ss.length
for(i=0;i<num;i++){
?? op=document.form1.ss.options[i]
?? if(op.value==va) op.selected=true;
}
}
</script>
<form name="form1">
<select name=ss>
?? <option value=1>111</option>
?? <option value=2>222</option>
?? <option value=3>333</option>
?? <option value=4>444</option>
</select>
<input type=button value=选择1 onclick="c_ss(1)">
<input type=button value=选择2 onclick="c_ss(2)">
<input type=button value=选择3 onclick="c_ss(3)">
<input type=button value=选择4 onclick="c_ss(4)">
</form>

////////////////////////////

<script>
function c_ss(va){
eval("document.all.a"+va+".selected=true");
}
</script>
<form name="form1">
<select name=ss>
?? <option id=a1 value=1>111</option>
?? <option id=a2 value=2>222</option>
?? <option id=a3 value=3>333</option>
?? <option id=a4 value=4>444</option>
</select>
<input type=button value=选择1 onclick="c_ss(1)">
<input type=button value=选择2 onclick="c_ss(2)">
<input type=button value=选择3 onclick="c_ss(3)">
<input type=button value=选择4 onclick="c_ss(4)">
</form>