using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

​

    public static void Main()

    {

        DateTime a = new DateTime(2019,04,05);

        DateTime b = new DateTime(2020,06,08);

        DateTime d = new DateTime(2018,06,08);

        List<DateTime> c = new List<DateTime>() {a, b ,d};

        foreach(var item in c.OrderBy(x => x.Date)) {

            Console.WriteLine(item);

        }

    }

}