Which of the following statements regarding abstract classes are true?

Given the following piece of code:

public class School{
        public abstract double numberOfStudent();
}

A. The keywords public and abstract cannot be used together.

B. The method numberOfStudent() in class School must have a body.

C. You must add a return statement in method numberOfStudent().

D. Class School must be defined abstract.

Which of the following class definitions defines a legal abstract class?

A. class A { abstract void unfinished() { } }

B. class A { abstract void unfinished(); }

C. abstract class A { abstract void unfinished(); }

D. public class abstract A { abstract void unfinished(); }

Which of the following declares an abstract method in an abstract Java class?

A. public abstract method();

B. public abstract void method();

C. public void abstract Method();

D. public void method() {}

E. public abstract void method() {}

Which of the following statements regarding abstract classes are true?

A. An abstract class can be extended.

B. A subclass of a non-abstract superclass can be abstract.

C. A subclass can override a concrete method in a superclass to declare it abstract.

D. An abstract class can be used as a data type.

E. All of the above