static void Main(string[] args)
        {
            Type a = typeof(A);
            Type b = typeof(B);
            Console.WriteLine(a.IsAssignableFrom(b));       //true
            Console.WriteLine(b.IsAssignableFrom(a));       //false
 
            Type c = typeof(Nullable<int>);
            Type d = typeof(int);
            Console.WriteLine(c.IsAssignableFrom(d));       //true
            Console.WriteLine(d.IsAssignableFrom(c));       //false
 
            Console.ReadLine();
        }
 
        class A { }
 
        class B : A { }