这个是继承与派生的实验，能使理解继承的含义，理解公有继承下基类成员对派生类成员和派生类对象的可见性，理解保护成员在继承中的作用，理解虚函数在类的继承层次中的作用-This is the inheritance and derived experiment, can understand the meaning of the succession, understanding the public under the base class inheritance derived class mem