What is the output of the following C++ program?#include using namespace std; class B { public: virtual void f() { cout

What is the output of the following C++ program?

#include <iostream>
using namespace std;
class B { public: virtual void f() { cout << "B"; } };
class D : public B { public: void f() { cout << "D"; } };
void g(B b) { b.f(); }
int main() {
    D d;
    g(d);
    B& r = d;
    r.f();
    return 0;
}