javascript 控制iframe

<table width="600" height="268" border="0" align="center">
<tr>
<td height="53" valign="top"> <div align="center">
<a href="#" onclick="document.getElementById('test').src='http://www.google.com'"> ... </div></td>
<td valign="top"><div align="center">
<a href="#" onclick="document.getElementById('test').src='http://www.baidu.com'"> ... </div></td>
<td valign="top"><div align="center">
<a href="#" onclick="document.getElementById('test').src='http://www.yahoo.com'"> ... </div></td>
</tr>
<tr>
<td height="209" colspan="3" valign="top"><iframe id="test" height="350" width="600" scrolling="no" align="center" border="0" frameborder="0" name="test" src="http://www.x-bai.com"></iframe></td>
</tr>
</table>