You are given a science question (easy-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.

Input: Consider Input: Many scientists are convinced that an increase of certain gases in the atmosphere is affecting global temperatures. What makes this hypothesis difficult to prove?
(A) Trees absorb these gases. (B) Global temperatures are rising. (C) Many variables affect global temperatures. (D) Many human activities produce these gases.

Output: C

Input: Consider Input: Compared to Earth, the Moon is
(A) drier. (B) larger. (C) heavier. (D) brighter.

Output: A

Input: Consider Input: A metal pan will heat up quickly when placed over a gas or electric burner. The metal pan is a good
(A) resistor. (B) insulator. (C) conductor. (D) accelerator.
Output: C