Question from the C++ - Fundamentals test

What does the following code display ?

class A {
public:
    virtual void hello() {cout << "A" << endl;}
};

class B : public A {
public:
    void hello() {cout << "B" << endl;}
};

void meet_value(A a1, A a2) {
    a1.hello();
    a2.hello();
}

 void meet_reference(A& a1, A& a2) {
    a1.hello();
    a2.hello();
}

int main() {
    B b; 
    A a;
    meet_value(a, b);
    meet_reference(a, b);
    return 0;
}