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.

[Q]: Scientists use ice cores to identify and explain previous climatic trends. By correlating climatic conditions recorded in the ice, with solid, nonsnow particles also found in the ice, scientists can help to predict the climatic impact of which phenomena?
(A) atmospheric carbon dioxide concentration changes (B) radioactive decay rate changes in the outer core (C) volcanic eruptions (D) magnetic pole reversals
[A]: C

[Q]: When do mutations help make an ecosystem more sustainable?
(A) when mutations decrease the number of individuals in an ecosystem (B) when mutations increase the number of individuals in an ecosystem (C) when mutations decrease the number of species in an ecosystem (D) when mutations increase the number of species in an ecosystem
[A]: D

[Q]: 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
[A]:
A