Polymorphism and Virtual Functions - General Questions

Can an abstract class be instantiated?

What makes a class abstract in C++?

Compile-time polymorphism is achieved by:

What will be the output of the program?

#include <iostream>
using namespace std;
class A { public: virtual int v() { return 1; } virtual ~A() {} };
class B : public A { public: int v() override { return 2; } };
int main() {
    A a = B();
    cout << a.v() << endl;
    return 0;
}

What will be the output of the program?

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