下列程序中横线处正确的语句应该是 。＃include using namespace std;class Base{ public;void fun(){cout< < “Base : : fun” < < endl;}};class Derived : public Base{public:void fun( ){_________ ; //显式调用基类的函数fun()，如非必要，标识符间不留空格cout < < “Derived : : fun” < < endl;}};