Facebook SDK -如何用c#添加字段

facebook SDK给出了传递注册表单字段的示例:

var fields = new object[]
     {
      new {name = "name"},
      new {name = "email"},
      new {name = "location"},
      new {name = "gender"},
      new {name = "birthday"},
      new {name = "password", view = "not_prefilled"},
      new {name = "like", description = "Do you like this plugin?",
                                         type = "checkbox",
                                         @default = "checked"},
      new {name = "phone", description = "Phone Number", type = "text"},
      new {name = "captcha"}
      };

我想添加一个自定义typeahead字段。如:

new {name = "live",       description = "Best Place to Live", type = "typeahead", categories = ("city, country, state_province")}

但是当我运行时，我在categories=语法上得到错误。说明类别是无效数组。我试过几种不同的语法，但似乎都行不通。添加类别的正确语法是什么?