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]: Which set contains kingdoms that contain only heterotrophs?   
 (A) Protists, Fungi (B) Bacteria, Animals (C) Plants, Fungi (D) Animals, Fungi
[EX A]: D

[EX Q]: Bones support the body. What pulls and pushes on bones to move them?  
 (A) blood (B) nerves (C) muscles (D) skin
[EX A]: C

[EX Q]: Most electricity in the United States is generated using coal, natural gas, nuclear energy, or hydropower. Which of these add carbon dioxide to the atmosphere?  
 (A) coal and natural gas (B) natural gas and nuclear energy (C) nuclear energy and hydropower (D) hydropower and coal
[EX A]:
A