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]: In the United States, which is responsible for ensuring the safety of the country's drinking water?  
 (A) Environmental Protection Agency (EPA) (B) Food and Drug Administration (FDA) (C) National Oceanic and Atmospheric Administration (NOAA) (D) Center for Disease Control (CDC)
[EX A]: A

[EX Q]: Because copper is a metal, it is  
 (A) liquid at room temperature (B) nonreactive with other substances (C) a poor conductor of electricity (D) a good conductor of heat
[EX A]: D

[EX Q]: Some jet airplanes fly in a layer of the atmosphere where temperature generally increases with altitude. What is this layer of the atmosphere?  
 (A) mesosphere (B) stratosphere (C) thermosphere (D) troposphere
[EX A]:
B