有如下程序： #include using namespace std class Base { private: void funl() const{cout$amp protected: void fun2() const{cout$amp public: void fun3() const{cout$amp } class Derived:protected Base { public: void fun4() const{cout$amp } int main() { Derived obj obj.funl() // ① obj.fun2() // ② obj.fun3() // ③ obj.fun4() // ④ return 0 } 其中有语法错误的语句是