how to get data from json?

I have controller

var subCategories = m_listsRepository.GetSubCategories(id);
 var items = subCategories.Select(x=>new MyDataNameAndId(){Id = x.Value, Name = x.Text});
 return Json(items);
 

And ajax:

$.ajax({
         url: urlString,
         type: 'POST',
         data: JSON.stringify({ id: districtId }),
         dataType: 'json',
         contentType: 'application/json',
         cache: 'false',
         success: function (data) {
             alert("success");
             $.each(data, function (key, MyDataNameAndId) {
                 alert(key);//== 0
                 alert(MyDataNameAndId);// then throws
                 $('select#ChangeOnsubCategoryId').append('<option value="0">Select One</option>');
 
                 $.each(MyDataNameAndId, function (index, manager) {
                     $('select#ChangeOnsubCategoryId').append(
                             '<option value="' + manager.Id + '">'
                             + manager.Name +
                             '</option>');
                 });
             });
         }
     });
 

what am I doing wrong?

UPDATE:
Controller is worked.
alert("success"); - is show
alert(key); - is show 0
alert(MyDataNameAndId); - not show.
I need generate in 'select#ChangeOnsubCategoryId' options from select#ChangeOnsubCategoryId

How do this? this understand?

I do not know how to show what passed json

json string:

[{"Id":"53","Name":"??????"}]
 

---