Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is corre…

Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is correct?1. A a = new A();2. A a = new B();3. B b = new A();4. B b = new B();