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 body is made up of many systems that interact with one another. For example, the skeletal system and the muscular system work together to help the body move. Which system works with the respiratory system to distribute oxygen to the body?  
 (A) muscular system (B) digestive system (C) lymphatic system (D) circulatory system
[EX A]: D

[EX Q]: Which lists the diameter of the planets in order from smallest to largest?  
 (A) Venus, Earth, Mercury, Mars (B) Earth, Mars, Venus, Mercury (C) Mars, Mercury, Earth, Venus (D) Mercury, Mars, Venus, Earth
[EX A]: D

[EX Q]: Some animals have behaviors that help them find food when little is available. Which best describes an animal with this type of behavior?  
 (A) a robin that builds a nest (B) an owl that calls at night (C) a duck that swims in water (D) a goose that migrates in winter
[EX A]:
D