运⾏以下C++代码，屏幕将输出“derived class”。
#include <iostream>
using namespace std;
class base {
public: virtual void show() {
cout << "base class" << endl;
}
};
class derived: public base {
public: void show() override {
cout << "derived class" << endl;
}
};
int main() {
base * b;
derived d;
b = & d;
b -> show();
return 0;
}
