You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Ex Input:
Rat snakes, Elaphe obsoleta, are a species made of many distinct populations in different areas. Each of the populations has different markings and colorings. Where would rat snakes most likely be gray?
(A) in a forest (B) in a swamp (C) in a gravel pit (D) in a corn field

Ex Output:
C

Ex Input:
How are green plants an important part of the carbon dioxide-oxygen cycle?
(A) They add oxygen to the soil. (B) They release oxygen into the air. (C) They fix carbon dioxide in the soil. (D) They store carbon dioxide in roots.

Ex Output:
B

Ex Input:
Which best explains why children resemble their parents?
(A) They eat the same foods. (B) They have similar DNA. (C) They speak the same language. (D) They have the same interests.

Ex Output:
B