单选题 Given the following program:#include <iostream>using namespace std;class Base {public: void fun ( ) { cout << "Base::fun" << endl; }};class Derived : public Base {public: void fun( ) { __________; cout << "Derived::fun" << endl; }};int main( ) { Derived d; d.fun( ); return 0;}After compiling and executing, it displays:Base::funDerived::funThen, the statement should be filled in underline is ( )