List 集合 转换为json 字符串
  public object Taoshow()
 {
 var i = pbll.PackShow();//list集合
 var lida = JsonConvert.SerializeObject(i); //转换成json字符串
 return lida;
 }
  function Tao() {
 $.ajax({
 url: "/Wangjie/Taoshow",
 type: "Get",
 dataType: "Json",
 success: function (obj) {
 for (var i = 0; i < obj.length; i++) {
 $("#Tao").append("<option value='" + obj[i].PT_id + "'>" + obj[i].PT_name + "</option>");
 }
 }
 })
 }