触发option事件的js怎么来写？

<div>
<select id="sel1" onchange="selChange(this)">
<option value='1'>A</option>
<option value='2'>B</option>
<option value='3'>C</option>
<option value='4'>D</option>
<option value='5'>E</option>
</select>
</div>
<script type="text/javascript" >
function selChange(obj)
{
var oi = obj.options[obj.selectedIndex].value;
var ot = obj.options[obj.selectedIndex].innerText;

var ajax = BuildAjaxModel();
ajax.onreadystatechange=function(data)
{
if(ajax.readyState==4)
{
data = ajax.responseText;
alert(data);
}
}