点击弹出下拉框

<TABLE >
<tr onclick="show()" id="222"><TD id="333">test1</TD><TD>test2</TD><TD>test3</TD><TD>test4</TD></tr>
<TR id="11111111" >
<TD id="33333333333333" >11</TD><TD>22</TD><TD>33</TD><TD>44</TD>
</TR>
</TABLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
var st = "<select onchange='gradeChange()'><option>111</option><option>222</option><option>test3</option><option>test4</option></select>";
 function gradeChange(){
        var objS =event.srcElement;
        //var id=event.parent();
        var a=objS.parentNode.parentNode;
        alert(a.id);
       // objS.innerHTML=a.id+"";
        objS.parentNode.innerHTML=a.id;
        var grade = objS.options[objS.selectedIndex].text;
        if (grade=="test3")
        alert(grade);
        //var grade = objS.options[objS.selectedIndex].grade;
       // alert(grade);
       }
function show(){
if (event.srcElement.tagName!="TD") return;
hide();
var elm = event.srcElement;
var st1 = "<option>"+elm.innerText+"</option>";
var st2 = "<option selected>"+elm.innerText+"</option>";
elm.innerHTML = st.replace(st1,st2);
event.cancelBubble=true;
}
function hide(){


}
//-->
</SCRIPT>