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:
Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?
(A) miles (B) meters (C) light years (D) astronomical units

Ex Output:
C

Ex Input:
One role of a producer in a food chain is to provide
(A) water for plants (B) sunlight for plants (C) nutrients for animals (D) shelter for animals

Ex Output:
C

Ex Input:
A student tosses a ball into the air. Which force causes the ball to fall back to the ground?
(A) gravity (B) magnetism (C) mechanical (D) friction

Ex Output:
A