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.

[Q]: Which two body systems are involved in inhaling oxygen and exhaling carbon dioxide?  
 (A) endocrine and skeletal (B) excretory and nervous (C) circulatory and respiratory (D) digestive and reproductive
[A]: C


[Q]: What form of energy is being used when a person pushes a wooden block across the floor?  
 (A) mechanical (B) magnetic (C) sound (D) electrical
[A]: A


[Q]: Which example describes an organism taking in nutrients?  
 (A) a dog burying a bone (B) a girl eating an apple (C) an insect crawling on a leaf (D) a boy planting tomatoes in a garden
[A]:
B