添加和移除下拉框的的内容

============html=============
<div class="demo1">
    <div>
        <div class="mb10">
            <input type="text" name="" id="txt"/><a id="add" href="javascript:;">添加</a>
        </div>
        <select name="" id="country">
            <option value="">中国人</option>
            <option value="">蒙古人</option>
            <option value="">朝鲜人</option>
        </select>
        <div class="pt10"><a id="del" href="javascript:;">删除</a></div>
    </div>
</div>
=============js=========
var country=document.getElementById(‘country‘);
var add=document.getElementById(‘add‘);
var txt=document.getElementById(‘txt‘);
var del=document.getElementById(‘del‘);

add.onclick=function () {
	var option=document.createElement(‘option‘);
	option.innerHTML=txt.value;
	country.appendChild(option);
}
del.onclick=function () {
	var index=country.selectedIndex;
	country.removeChild(country[index]);
}