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 model of the Moon would be different from a model of Earth in that the Moon should
(A) be smaller than Earth. (B) have a source of light inside. (C) have a smoother surface than Earth. (D) have fewer impact craters on the surface.

Ex Output:
A

Ex Input:
What is a common use of the mineral graphite?
(A) to make glass (B) as a source of iron (C) to make pencil leads (D) as a household cleaner

Ex Output:
C

Ex Input:
A student needs to find the mass of an atom. The numbers of which atomic particles determines the mass of the atom?
(A) only its protons (B) only its electrons (C) both its protons and neutrons (D) both its neutrons and electrons

Ex Output:
C