using System;

using System.Collections.Generic;

using System.Threading.Tasks;

public class Program

{

    public async static Task Main()

    {

        var list = new List<Task<IEnumerable<object>>>{

            Task.FromResult<IEnumerable<object>>( new List<Product>{ new Product{} } ),         

            Task.FromResult<IEnumerable<object>>( new List<Category>{ new Category{} } ),

        };

        await convertTasks(list);

    }

    static async Task<List<string>> convertTasks(List<Task<IEnumerable<object>>> taskList) 

     {

         List<string> jsonresult = new List<string>();

         foreach (var task in taskList) 

         {

             var result = await task;

             foreach (var _unknownObject in result)

             {

                //jsonresult.Add( new JavaScriptSerializer().Serialize(_unknownObject));

                 Console.WriteLine(_unknownObject);

             }

         }

         return jsonresult;

     }

}

​

public class Product{}

​

public class Category{}