using System;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var source = new { Data = (object)new Cat { MiaoLoudness = "So loud" } };

        var serialized = JsonConvert.SerializeObject(source);

        Console.WriteLine(serialized);

    }

    public abstract class Animal

    {

        public string Name { get; set; }

    }

    public class Dog : Animal

    {

        public string WoofLoudness { get; set; }

    }

    public class Cat : Animal

    {

        public string MiaoLoudness { get; set; }

    }

}