the contrapositive of the statement "if you study hard, then you will pass the exam" is : A. if you study hard, then you will fail the exam

B. if you fail the exam, then you did not study hard

C. if you pass the exam, then you studied hard

D. if you do not pass the exam, then you did not study hard

please only choose one not two choices

i know that both B and D are correct but then why the instructor put these two choices in the exam? is D more correct than B? or are they really both correct?

urgent please please