这样一个效果为什么不能实现？急盼高手解答

[yzflying]

我有在一个表单里面有两个下拉框:
<td><select name="select" onchange="show()">
<option value="1" selected>Toilet seat</option>
<option value="2">Cabinet</option>
<option value="3">Mirror frame</option>
<option value="4">Basin</option>
<option value="5">Faucet</option>
<option value="6">Shower head</option>
<option value="7">Accessories</option>
</select></td>
另外一个：
<tr>
<td align="center">产品二级类别：</td>
<td><select name="select2">
<option value="1" selected>Wooden toilet seat</option>
<option value="2">MDF flat toilet seat</option>
<option value="3">Pressed wood toilet seat</option>
<option value="4">Polyresin toilet seat</option>
<option value="5">Fabric decor toilet seat</option>
</select></td>
</tr>
我想用一个onchange事件，实现这样的一个效果，既当第一个select的值等于的时候显示下面一个select，等于其他则不显示，我这样做为什么不行？

<select name="select" onchange="show()">

<script language=javascript>
function show(){
if (document.form.select.value==1){
document.write('
<tr>
<td align="center">产品二级类别：</td>
<td><select name="select2">
<option value="1" selected>Wooden toilet seat</option>
<option value="2">MDF flat toilet seat</option>
<option value="3">Pressed wood toilet seat</option>
<option value="4">Polyresin toilet seat</option>
<option value="5">Fabric decor toilet seat</option>
</select></td>
</tr>')}
}
</script>

[qiushuiwuhen]

<table>
<tr><td><select name="select" onchange="showList.style.display=(value==1?'inline':'none')">
<option value="1" selected>Toilet seat</option>
<option value="2">Cabinet</option>
<option value="3">Mirror frame</option>
<option value="4">Basin</option>
<option value="5">Faucet</option>
<option value="6">Shower head</option>
<option value="7">Accessories</option>
</select></td>
</tr>
<tr id=showList>
<td align="center">产品二级类别：</td>
<td><select name="select2">
<option value="1" selected>Wooden toilet seat</option>
<option value="2">MDF flat toilet seat</option>
<option value="3">Pressed wood toilet seat</option>
<option value="4">Polyresin toilet seat</option>
<option value="5">Fabric decor toilet seat</option>
</select></td>
</tr>
</table>

[yzflying]

我服，分全给 ！