There are 9 fictions and 6 non-fictions. How many cases are there such that 2 fictions and 2 non-fictions are selected from them?
Options:
(A) 90
(B) 120
(C) 540
(D) 180
(E) 200 Stream of consciousness:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Number of ways of selecting 2 fiction books = 9C2
Number of ways of selecting 2 non fiction books = 6C2
9C2 * 6C2 = 36 * 15 = 540
Thus, the answer is (C).