asp.net项目下的web service返回json数据问题

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.ServiceModel.Web;
using System.Text;
using System.Web;
using System.Web.Script.Serialization;
using System.Web.Script.Services;
using System.Web.Services;
using System.Web.UI.WebControls;

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
[System.Web.Script.Services.ScriptService]

public class WebService : System.Web.Services.WebService
{
   [WebMethod]
    [ScriptMethod(ResponseFormat = ResponseFormat.Json, UseHttpGet = true)]
    public void GetStores(string deliveryStartTime, string deliveryEndTime, bool is20To22 = false, string cityPOSCodePrefix = "960")
    {
        var storeListJson = new StringBuilder();

        //
        var storeList = GetStoreList(deliveryStartTime, deliveryEndTime, is20To22, cityPOSCodePrefix);
        storeListJson.Append("[");
        foreach (var store in storeList)
        {
            string format = "{{\"Value\":\"{0}\", \"Text\":\"{1}\"}}";

            storeListJson.Append(string.Format(format, store.Value.ToString(), store.Text.ToString()));
            storeListJson.Append(",");
        }
        storeListJson.Remove(storeListJson.Length - 1, 1);
        storeListJson.Append("]");
        //

        Context.Response.Clear();
        Context.Response.ContentType = "text/json; charset=utf-8";
        //Context.Response.AddHeader("content-disposition", "attachment; filename=export.json");
        //Context.Response.AddHeader("content-length", storeListJson.Length.ToString());
        Context.Response.Flush();
        Context.Response.Write(storeListJson);
    }
 }

var url = "/webservice.asmx/GetStores?cityPOSCodePrefix=" + cityPOSCodePrefix + "&deliveryStartTime=" + deliveryStartTime
                + "&deliveryEndTime=" + deliveryEndTime + "&is20To22=" + is20To22;

$.ajax({
                url: url,
                type: ‘get‘,
                async: false,
                contentType: ‘text/json; charset=utf-8‘,
                success: function (result) {
                    //alert(result.d[0]);
                    var storeListString = "";
                    var storeLiValueStart = "<li style=\"float: left; margin-left: 40px; margin-top: 8px; width: 120px; border-radius: 8px; background-color: #FFF; border: 2px solid rgb(0,119,175);color:#0077af; padding: 4px 0px; text-align: center; cursor: pointer\" id=\"";
                    var storeLiValueEndAndTextStart = "\">";
                    var storeLiTextEnd = "</li>";

                    for (var i = 0; i < result.length; i++) {
                        storeListString += storeLiValueStart;
                        storeListString += result[i].Value;
                        storeListString += storeLiValueEndAndTextStart;
                        storeListString += result[i].Text;
                        storeListString += storeLiTextEnd;
                    }

                    $("#storeListTest").html(storeListString);
                }

    <webServices>
      <protocols>
        <add name="HttpGet" />
      </protocols>
    </webServices>