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:
What is the complementary base to cytosine in DNA?  
 (A) uracil (B) thymine (C) guanine (D) adenine

Ex Output:
C


Ex Input:
A thermometer is best used to measure  
 (A) air pressure. (B) kinetic energy. (C) potential energy. (D) wind movement.

Ex Output:
B


Ex Input:
Which animal is preparing for a seasonal change in the environment?  
 (A) a bat flying at night (B) a deer drinking water (C) an owl eating a mouse (D) a squirrel storing nuts

Ex Output:

D