select下拉显示数量控制

<select onmouseover="jxq(1);" onmouseout="jxq(2);" size="1"> <option>1111</option></select>
<select onmouseover="jxq(1);" onmouseout="jxq(2);" size="1"> <option>2222</option></select>
<select onmouseover="jxq(1);" onmouseout="jxq(2);" size="1"> <option>3333</option></select>
<select onmouseover="jxq(1);" onmouseout="jxq(2);" size="1"> <option>4444</option></select>
<select onmouseover="jxq(1);" onmouseout="jxq(2);" size="1"> <option>5555</option><option>6666</option></select>

<script type="text/javascript">
// <![CDATA[
function jxq(s){
if (s == 1){
document.all.jia.size="3";
}else{
document.all.jia.size="1";
}
}
// ]]></script>