<script>
function aa()
{
b.style.display="none";
c.style.display="none";
}
</script>
<div id="a"><select onchange="aa();"><option><option>A</option></select><br><hr></div>
<div id="b"><select><option><option>A</option></select><br><hr></div>
<div id="c"><select><option><option>A</option></select><br><hr></div>
function aa()
{
b.style.display="none";
c.style.display="none";
}
</script>
<div id="a"><select onchange="aa();"><option><option>A</option></select><br><hr></div>
<div id="b"><select><option><option>A</option></select><br><hr></div>
<div id="c"><select><option><option>A</option></select><br><hr></div>
onchange=setValue('a',,b');function setValue(a,b){
eval('form1.'+a).value="";
eval('form1.'+b).value="";}