如何选中复选框以后改变所在行的背景？

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<SCRIPT LANGUAGE="JavaScript">
<!--
function changeback(obj)
{
if(obj.checked)
obj.parentNode.parentNode.bgColor='#f4f4f4';
else
obj.parentNode.parentNode.bgColor='#ffffff';
}
//-->
</SCRIPT>
</HEAD><BODY>
<TABLE width="100%" border=1>
<TR>
<TD><INPUT TYPE="checkbox" NAME="" onpropertychange="changeback(this)"></TD>
<TD>1</TD>
</TR>
<TR>
<TD><INPUT TYPE="checkbox" NAME="" onpropertychange="changeback(this)"></TD>
<TD>2</TD>
</TR>
<TR>
<TD><INPUT TYPE="checkbox" NAME="" onpropertychange="changeback(this)"></TD>
<TD>3</TD>
</TR>
</TABLE>
</BODY>
</HTML>