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]: The most significant human-induced impact on Earth's atmosphere comes from the use of which energy resource?  
 (A) flowing water (B) fossil fuels (C) sunlight (D) winds
[EX A]: B

[EX Q]: The phases of the Moon are daily changes in the appearance of the Moon. One reason Moon phases occur is because the Moon reflects sunlight. Which is another reason that the phases of the Moon occur?  
 (A) Earth is tilted on the axis. (B) The Moon rises and sets. (C) The Moon orbits Earth. (D) Earth orbits the Sun.
[EX A]: C

[EX Q]: Which body system sends electrical signals to all other body systems?  
 (A) circulatory system (B) digestive system (C) muscular system (D) nervous system
[EX A]:
D