4. Consider the following class diagram and answer the following: Some of the following assignments are legal and some are illegal. Find out which are legal or illegal. Explain why any statement is legal or illegal? a) Animal al = new Mammal(); b) Animal a2 = new Parrot(); c) Birds a3 = new Mammal(); d) Birds a4 = new Pigeon(); e) Parrot a5 = new Birds()