<form name="form1" method="post" action="">
<select name="select">
<option value="1111">1111</option>
<option value="2222">2222</option>
<option value="3333">3333</option>
<option value="4444">4444</option>
</select>
<input type="button" name="Button" value="Button" onClick="form1.select.options[2].selected=true">
</form>
<select name="select">
<option value="1111">1111</option>
<option value="2222">2222</option>
<option value="3333">3333</option>
<option value="4444">4444</option>
</select>
<input type="button" name="Button" value="Button" onClick="form1.select.options[2].selected=true">
</form>
<select name="select">
<option value="1111">1111</option>
<option value="2222">2222</option>
<option value="3333">3333</option>
<option value="4444">4444</option>
</select>
<input type="button" name="Button" value="Button" onClick="form1.select.selectedIndex=2">
</form>
<select name="select2" onchange="addimage();">
<option value="" selected>贴图</option>
<option value="image/0001.gif">礼物</option>
<option value="image/cuts1841.gif">书</option>
<option value="image/liu5.gif">加油</option>
<option value="image/wy4.gif">足球少女</option>
</form>
<input type="button" name="Button" value="Button" onClick="input.select2.selectedIndex=2">
</form>
<select name="select2" onchange="addimage();">
<option value="" selected>贴图</option>
<option value="image/0001.gif">礼物</option>
<option value="image/cuts1841.gif">书</option>
<option value="image/liu5.gif">加油</option>
<option value="image/wy4.gif">足球少女</option>
</select>
<script>
document.imput.select2.value="指定值";//如:image/0001.gif
</script>
</form>
或document.form1.select1.selectindex=2