Found a question, can anyone help?

Question

How can you force a class to implement only features of our class?
a. Only abstract class
b. Only interface
c. Abstract class or interface
d. We cannot

Answer 1

Isn't it the final class you are looking for?
Final classes cannot be extended so no functionality can be added.

Answer 2

with an interface the childclass has to implement all the parentclass methods

with an abstract class the childclass gets all methods from its parent and has to overwrite all abstract methods

Answer 3

Only abstract class. Once a class declared abstract is derived from, all of the classes (abstract) methods are forced to be declared.