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:
A biological community is made up of all the
(A) populations living in an area (B) natural resources present in an area (C) members of a species on Earth (D) environments on Earth

Ex Output:
A

Ex Input:
Earth is composed of layers of material with different properties. Which of the following is most likely to be in constant motion?
(A) core (B) mantle (C) oceanic crust (D) continental crust

Ex Output:
B

Ex Input:
What causes the most soil and rock erosion?
(A) sun (B) wind (C) water (D) gravity

Ex Output:
C