What Will Have to Change If the Instance Variables Month

Multiple Choice

What will have to change if the instance variables month and day of the Date class are replaced by the single instance integer variable dayOfTheYear?

A) The implementation of the methods will change, but the interface will not need to change.
B) The implementation of getDay will not change, but the implementations of the other methods will not change and the interface will not change.
C) The interface will need to change to remove setMonth, but no other parts of the interface will change.
D) All of the interface will need to be changed when the instance variables change.