请教一个小问题

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD></HEAD><BODY>
<div align="center" id="aa">Test attachEvent and detachEvent
</div>
<TITLE> Test attachEvent and detachEvent </TITLE>
<SCRIPT LANGUAGE="JavaScript">
var fnclick=function (){
alert("checked");
}
var oB=document.getElementById("aa");
oB.attachEvent("onclick",fnclick);</SCRIPT>
</BODY>
</HTML>