Sample

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

namespace Nikolai
{
    class A
    {
        public virtual event Action<string> VirtualEvent;

        public void CallVirtualEvent()
        {
            VirtualEvent?.Invoke("Class A");
        }
    }

    class ChildA : A
    {
        public override event Action<string> VirtualEvent;

        public new void CallVirtualEvent()
        {
            VirtualEvent?.Invoke("Class ChildA");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            A a = new ChildA();
            a.VirtualEvent += (string e) => Console.WriteLine(e);
            a.CallVirtualEvent();
        }
    }
}