<table border="0" width="34%" cellspacing="0" cellpadding="0">
<form method="POST" action="" name=form1>
<tr>
<td width="43%">
<select size="1" name="selA" style="width:100%" onchange="form1.selB.options(this.value-1).selected=true">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option></select>
</td>
<td width="44%">
<select size="1" name="selB" style="width:100%">
<option value="A">A</option>
<option value="B">B</option>
<option value="C">C</option>
</select>
</td>
<td width="12%">
<input type="submit" value="提交" name="B1">
</td>
</form>
</tr>
</table>
<form method="POST" action="" name=form1>
<tr>
<td width="43%">
<select size="1" name="selA" style="width:100%" onchange="form1.selB.options(this.value-1).selected=true">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option></select>
</td>
<td width="44%">
<select size="1" name="selB" style="width:100%">
<option value="A">A</option>
<option value="B">B</option>
<option value="C">C</option>
</select>
</td>
<td width="12%">
<input type="submit" value="提交" name="B1">
</td>
</form>
</tr>
</table>
<tr>
<td><select name=a onchange="b.options[this.selectedIndex].selected=true">
<option>1</option>
<option>2</option>
<option>3</option>
</select>
</td><td>
<select name=b>
<option>a</option>
<option>b</option>
<option>c</option>
</select></tr></form>
</table>