AJAX JSON未检索值

From my controller I am passing a list called ccdata through JSON. It only has 1 record which is a list.

    return Json(rpata, JsonRequestBehavior.AllowGet);

In my view, I tried to pull the value of FirstName and LastName but got an error - 'FirstName.0' is null or not an object:

    $.ajax({
      type: "GET",
      contentType: "application/json; charset=utf-8",
      url: '@Url.Action("GetRpInfo", "PgController")',
                 data: { ID: ID },
                 dataType: "json",
                 success: function (rpdata) {

                    var rpinfo = rpdata.FirstName[0] + " " + repdata.LastName[0];

              }
   });

Isn't this what you need?

var rpinfo = rpdata[0].FirstName + " " +rpdata[0].LastName

You can debug the result to see what rpdata contains.