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 of these is the center of our solar system?  
 (A) Mars (B) The moon (C) Jupiter (D) The sun
[EX A]: D

[EX Q]: Two atoms of oxygen combine to form pure oxygen gas. What is the electrical charge of the O_{2} molecules?  
 (A) positive (B) negative (C) neutral (D) variable
[EX A]: C

[EX Q]: A student notices dogs have more fleas in the summer than in the winter. Based on these observations, which is the most logical question for the student to investigate?  
 (A) How does wind affect the amount of fleas on dogs? (B) How does diet affect the amount of fleas on dogs? (C) How does rain affect the amount of fleas on dogs? (D) How does temperature affect the amount of fleas on dogs?
[EX A]:
D