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.

Ex 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.

Ex Output:
C

Ex Input:
Diamonds are sometimes used as the tips of drill bits. Which physical property of a diamond MOST likely makes it a good cutting tool?
(A) its electrical properties (B) its thermal properties (C) its hardness (D) its density

Ex Output:
C

Ex Input:
Which health condition is an infectious disease?
(A) pneumonia caused by microorganisms (B) heart problem caused by a high-fat diet (C) lung cancer caused by smoking (D) eye damage caused by ultraviolet light

Ex Output:
A