不能在子类或外部类发布C#事件代码分析

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

namespace EventStudy
{
    class Program
    {
        static void Main(string[] args)
        {
        }
    }

    class Base
    {
        private Action _testEventB;

        public event Action TestEventA;

        public event Action TestEventB
        {
            add
            {
                _testEventB += value;
            }
            remove
            {
                _testEventB -= value;
            }
        }

        protected void OnTestEventA()
        {
            var testEventA = this.TestEventA;

            testEventA();
        }

        protected void OnTestEventB()
        {
            var testEventB = _testEventB;

            testEventB();
        }
    }

    class Child : Base
    {
        public void Do()
        {
            //this.TestEventA();不能这样访问
        }
    }
}

protected void OnTestEventA()
        {
            var testEventA = this.TestEventA;

            testEventA();
        }