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 body systems are most involved in the response when someone stubs his or her toe?  
 (A) nervous and muscle (B) muscle and endocrine (C) nervous and digestive (D) reproductive and circulatory
[EX A]: A

[EX Q]: What happens to the water vapor in an air mass as it ascends?  
 (A) It freezes. (B) It condenses. (C) It vaporizes. (D) It polarizes.
[EX A]: B

[EX Q]: Which best describes the orbit of the Moon around Earth?  
 (A) circular with a period of about one month (B) circular with a period of about one week (C) elliptical with a period of about one month (D) elliptical with a period of about one week
[EX A]:
C