asp.net 母版页中二级级联有关问题_ASP.NET

asp.net 母版页中二级级联问题
二级级联的代码放在普通页面中就能够显示出来，没有错误。
但是放到母版页中就显示不出来了！

求各位高手帮忙解决！谢谢！

js代码如下：

JScript code

 var cityList = new Array( );       cityList['北京'] = ['朝阳区','东城区','西城区', '海淀区','宣武区','丰台区','怀柔','延庆','房山'];     cityList['上海'] = ['宝山区','长宁区','丰贤区', '虹口区','黄浦区','青浦区','南汇区','徐汇区','卢湾区'];     cityList['广州'] = ['天河区','海珠区','南沙区', '白云区','嘉湾区','越秀区','黄埔区','罗岗区','番寓区','花都区'];     cityList['深圳'] = ['福田区', '罗湖区', '盐田区', '宝安区', '龙岗区', '南山区', '深圳周边'];     cityList['重庆'] =['俞中区', '南岸区', '江北区', '沙坪坝区', '九龙坡区', '渝北区', '大渡口区', '北碚区', '巴南区', '万盛区', '涪凌', '江津'];     cityList['天津'] = ['和平区', '河西区', '南开区', '河北区', '河东区', '红桥区', '塘古区', '开发区', '西青区', '津南区','东丽区'];            function changeCity( )  {     var province=document.getElementById("province").value;      document.getElementById("city").options.length=0;     for (var i in cityList)      {            if (i == province)             {                for (var j in cityList[i])                 {                     document.getElementById("city").options.add(new Option(cityList[i][j], cityList[i][j]));                }            }       }     document.getElementById("city").options.selctIndex=0;  }    function loadAll( )  { for (var i in cityList)         { document.getElementById("province").options.add(new Option(i, i));         }        document.getElementById("province").selectedIndex = 0;   }

asp.net普通页面中能够显示，代码如下：

HTML code

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312"/>    <title>无标题页</title>   <script src="JS/citys.js" type="text/javascript"></script>  </head><body>    <form id="myform" runat="server">         <select id="province" runat="server" onchange="changeCity()">            <option>----省份----</option>        </select>        <select id="city" runat="server">            <option>----城市----</option>        </select>        <script type="text/javascript">loadAll()</script>     </form>     </body></html>

asp.net母版页中就不能显示了，各位帮帮忙，代码如下：

HTML code

<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" Title="无标题页" %><asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">    <script src="JS/citys.js" type="text/javascript"></script>    </asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">    <select id="province" runat="server" onchange="changeCity()">        <option>----省份----</option>    </select>    <select id="city" runat="server">        <option>----城市----</option>    </select>    <script type="text/javascript">loadAll()</script>    </asp:Content>