Json返回查询的数据，前台ajax获取

[WebMethod]
public string GetCusCode()
{
DataTable dt = C_c.SelectT("select CusCode from Customer");
string jsonResult = null;
if (dt.Rows.Count > 0)
{
jsonResult = JsonConvert.SerializeObject(dt);
}
return jsonResult;
}

<pre name="code" class="html">$(document).ready(function () {

var rowOption = "";
$.ajax({
type: "post",
contentType: "application/json",

url: "/webservice/WebService.asmx/GetCode",
data: "{}",
dataType: "json",
success: function (result) {
var jsonList = eval(result.d);
alert(jsonList[0].Code);
for (var i = 0; i < jsonList.length; i++) {
rowOption += "<option value=" + jsonList[i].Code + ">" + jsonList[i].Code + "</option>";
}

$("#cusselect ").empty();
$("#cusselect ").append(rowOption);
}
});
}）;