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&nbsp;&nbsp;
    <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";
            }
        }