using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var items = new List<AppModuleInstance>() {

            new AppModuleInstance{ Id = 1, Title = "Test 1", ModuleCd = "EXAM" },

            new AppModuleInstance{ Id = 2, Title = "Test 2", ModuleCd = "EXAM" },

            new AppModuleInstance{ Id = 3, Title = "Test 3", ModuleCd = "EXAM" }

        };

        var exams = items.Select(i => i.ConvertToChild()).Cast<Exam>();

    }

    public class AppModuleInstance

    {

        public int Id { get; set; }

        public string Title { get; set; }

        public string ModuleCd { get; set; }

        public AppModuleInstance ConvertToChild()

        {

            return ConvertToChild(this);

        }

        public AppModuleInstance ConvertToChild(AppModuleInstance instance)

        {

            if (instance == null || string.IsNullOrWhiteSpace(instance.ModuleCd)) return instance;

            if (instance.ModuleCd == "EXAM"){

                var x = new Exam();

                x.Id = instance.Id;

                x.Title = instance.Title;

                x.ModuleCd = instance.ModuleCd;

                return x;

            } else {

                throw new NotImplementedException();

            }

        }

    }

    public class Exam : AppModuleInstance

    {

        public int Duration { get; set; }

    }

}