点击按钮选择下拉框

<input type="button" value="选择城市" id="btn16" />
        <select name="" id="ss">
            <option value ="1">武汉</option>
            <option value ="2" id="op1">北京</option>
            <option value ="3">上海</option>
        </select>
        <script>
            function my$(id){
                return document.getElementById(id);
            }
            my$("btn16").onclick=function(){
                my$("op1").selected=true;
            }
        </script>
        <textarea rows="30" cols="10" id="tt" readonly>
            ndofnsdfnosd
            ndfosnfosfij
            ndflsdfsjdf
            ndfosfsnd
            snfosdfos
        </textarea>
        <input type="button" value="注册" id="btn17" />
        <script type="text/javascript">
            my$("btn17").onclick=function(){
                my$("tt").value="lalallala";//推荐使用value,因为看成了是表单的标签
                //my$("tt").innerText="lalallala";
            };
        </script>