重复成员函数的调用
一道作业题，想了很久都不知道怎么做，内容如下：
class Base { public: virtual void mf1() = 0; virtual void mf1(int x); virtual void mf2(); void mf3(); void mf3(double x); int t;};class Derived: public Base { public: virtual void mf1(); //using Base::mf1; //using Base::mf3; void mf3(); void mf4(); using Base::t;};int main(){ Derived d; int x; d.mf1();//1 d.mf1(x);//2 d.mf2();//3 d.mf3();//4 d.mf3(x);//5}