Which statement is true when a superclass has protected instance variables?

a. A subclass object can assign an invalid value to the superclass’s instance variables, thus leaving an object in an
inconsistent state.
b. Subclass methods are more likely to be written so that they depend on the superclass’s data implementation.
c. We may need to modify all the subclasses of the superclass if the superclass implementation changes.
d. All of the above.

d. All of the above.