asp+ajax 出现乱码如何解决？

index.asp
VB code:
<%@LANGUAGE="VBSCRIPT.Encode" CODEPAGE="65001"%>
<%

Db="data/test12.mdb"
ConnStr = "Provider = Microsoft.Jet.OLEDB.4.0;Data Source = " & Server.MapPath(Db)
On Error Resume Next
Set Conn = Server.CreateObject("ADODB.Connection")
Conn.Open ConnStr

function getBigClass()
dim sql
sql = "select * from BigClass"
set rs = server.CreateObject("adodb.Recordset")
rs.open sql,conn,1,3
do while not rs.eof
BigClass= BigClass&"<option value='"&rs("BigClassId")&"'>"&rs("BigClassName")&"</option>"
rs.movenext
loop
Response.Write BigClass
End function
%>

<script>
function sendajax(BigClassId)
{
var ajaxObj;
var values;
if(window.XMLHttpRequest){
ajaxObj = new XMLHttpRequest();
} else if(window.ActiveXObject){
ajaxObj = new ActiveXObject("Microsoft.XMLHTTP");
}
if(ajaxObj){
//alert("创建ajax成功!");

}

ajaxObj.open("GET","getSmallClass.asp?BigClassId="+BigClassId,true);
ajaxObj.onreadystatechange = function(){
if(ajaxObj.readyState==4){
if(ajaxObj.status==200)