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]: One of the main causes of acid rain is
(A) Waste from nuclear power plants (B) Spills from chemical manufacturing plants (C) Gases from burning fossil fuels (D) Gases from aerosol spray cans
[EX A]: C

[EX Q]: When iron combines with oxygen in a moist environment, rust forms because of a
(A) chemical reaction. (B) physical reaction. (C) change in density. (D) change in temperature.
[EX A]: A

[EX Q]: According to the rock cycle, when liquid magma cools into a solid, what is formed?
(A) lava (B) glaciers (C) igneous rock (D) metamorphic rock
[EX A]:
C