城市二级菜单，jquery  xml 如何选择北京显示相应的城市，下面是一部分xml格式
 <province>
    <title>北京</title>
    <item>
        <city>东城</city>
        <city>西城</city>
        <city>崇文</city>
        <city>宣武</city>
        <city>朝阳</city>
        <city>丰台</city>
        <city>石景山</city>
        <city>海淀</city>
        <city>门头沟</city>
        <city>房山</city>
        <city>通州</city>
        <city>顺义</city>
        <city>昌平</city>
        <city>大兴</city>
        <city>平谷</city>
        <city>怀柔</city>
        <city>密云</city>
        <city>延庆</city>
    </item>
</province>
 <select id="DropProvince" style="width:60px;">
            <option>请选择</option>
        <select>
        <select id="sCity" style="width:60px;">
        <select>

//获得省
$(document).ready(function () {
            $.ajax({ url: "serverDoc.xml",
                success: function (xml) {
                    $(xml).find("title").each(function () {
                        var t = $(this).text(); //this->
                        $("#DropProvince").append("<option>" + t + "</option>");
                    });
                }
            });
            //获得市。。不能获取，
            $("#DropProvince").change(function () {
                $("#sCity>option").remove();
                var pname = $("#DropProvince").val();
                $.ajax({ url: "serverDoc.xml",
                    success: function (xml) {
                        $(xml).find("province[val=" + pname + "] city").each(function () {
                            $("#sCity").append("<option>" + $(this).text() + "</option>");
                        });
                    }
                });
            });
        });

哪位帮忙看看？