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 Q]: Which two protein molecules are essential for muscle contraction and relaxation?
(A) actin and myosin (B) collagen and tubulin (C) hemoglobin and myoglobin (D) amylase and polymerase
[EX A]: A

[EX Q]: The Great Ocean Conveyer ocean current system runs north through the Atlantic from the equatorial region. If this current got disrupted, North American and European climates would become
(A) rainier. (B) colder. (C) windier. (D) more humid.
[EX A]: B

[EX Q]: Scientists go to a lake once a month to take samples of water. They are most likely studying the
(A) number of fish. (B) depth of the lake. (C) quality of the water. (D) speed of the water.
[EX A]:
C