Wojtek

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

class A
{
    public void hello()

    {
        Console.WriteLine("hello");
    }
}

class B : A { }

class C { }

class Test<T> where T : A
{
    T obj;
    public Test(T o)
    {
        obj = o;
    }

    public void sayHellow()
    {
        obj.hello();
    }
}

class BaseClassConstraintDemo
{
    public static void Main()
    {
        A a = new A();
        B b = new B();
        C c = new C();

        Test<A> t1 = new Test<A>(a);
        t1.sayHellow();

        Test<B> t2 = new Test<B>(b);
        t2.sayHellow();

        Test<C> t3 = new Test<C>(c);
        t3.sayHellow();
    }
}