Mike is right.
Extending refers to creating a subclass.
Modifying refers to altering the existing class.
If your FBN is anything like mine was, you will have deprecated method calls inside private methods.
Ask yourself how you would overcome this in a subclass without cutting and pasting code from the private method in Data.
There are a few other clear reasons why you may want to take one path rather than the other - I won't state them here because you will come across them for yourself.
As with much else in the exam, there is no one right way to do things. There may be quite a few wrong ones
but as long as you don't pick one of those and can fight your corner come design choices time and essay exam time, you'll be fine.