Which of the following statements are true about abstract classes?
◦ A subclass can be abstract even if its superclass is concrete.
◦ An abstract class cannot be instantiated using the new operator.
◦ It is possible to declare an abstract class that contains no abstract methods.
◦ An abstract method cannot be contained in a nonabstract class.
◦ If a subclass of an abstract superclass does not implement all the abstract methods, the subclass must be declared abstract.