Question: What is the single responsibility principle?

1. Software entities should be open for extension, but closed for modification.
2. Entities must depend on abstractions, not on concrete implementations.
3. Objects in a program should be repleaceble with instances of their subtypes without altering the correctness of that programm.
4. A class should have only a single responsibility - that is, only changes to one part of the software's specification should be able to affect the specification of the class.

Answer: The correct answer of the above question is Option D:A class should have only a single responsibility - that is, only changes to one part of the software's specification should be able to affect the specification of the class.