js 通过单选框 展开和收缩 下拉框

input控件

<%--选择是否入住单选框，动态显示宿舍下拉框--%>
<div id="c">
<input type ="radio" id="r1" name ="g" onclick ="cc1()" />是  
<input type ="radio" id="r2" name ="g" />否<br />
<select size ="5" style ="display :none " id ="s1">
<option >请选择</option>
<option >男生寝室</option>
<option >女生寝室</option>
</select>
</div>

js代码

function cc1() {
var q4 = document.getElementById("r1");
var q5 = document.getElementById("r2");
var q6 = document.getElementById("s1");
if (q4.checked == true) {
q6.style.display = "block";
}
else
{
q6.style .display ="none";
}
}