a. To ensure that the same license is not being used illegally
b. To ensure Windows is configured property
c. To ensure that the hardware is validated by Microsoft
d. To ensure that Windows is not being used for illegal activity
The answer is a to ensure that the same license is not being used more than once.
Idea for such textbook question is to pamper to what the textbook wanted from you as the answer, (A) is most likely, but all choices are possibles.
A. is the best choice of the ones you listed. A better statement would be “To prevent COPY WRITE Violations”