<script language="javascript">
onload=show;
function show(){
//this.options[this.selectedIndex].value
var a=document.form1.a.value;
var b=document.form1.x.value;
document.images.pic.src=a+b+".gif";
}
</script>
<form name="form1">
<select name="a" onchange="show();">
<option value="t" selected>a</option>
<option value="f">b</option>
</select>
<select name="x" onchange="show();">
<option value="1" selected>1</option>
<option value="2">2</option>
</select>
</form><br><br>
<img name="pic" src="" border="0">
