已定义基类A和派生类B: class A { ptivate: int x; protected: int y; public: int z; void ShowA( ) { cout << x << y << z << endl; } }; class B : protected A // 保护继承 { private : int a; protected: int b; public: int c; void ShowB( ) { ShowA( ); cout << a << b << c << endl; } }; 再定义B的派生类C: class C : public B { public: int m; void fun( ) { x = 5; y = 5; z = 5; ShowA( ); } // 访问基类A的成员 }; 函数fun( )中错误的语句是( )。