instruction:
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.
question:
All of the different organisms interacting in a pond make up  
 (A) a community (B) a population (C) the water cycle (D) the habitat
answer:
A


question:
Which organ is made mostly of muscle?  
 (A) heart (B) lung (C) ear (D) brain
answer:
A


question:
Which four elements make up most of the human body?  
 (A) oxygen, carbon, hydrogen, nitrogen (B) silicon, calcium, oxygen, aluminum (C) carbon, sodium, hydrogen, oxygen (D) sulfur, phosphorous, calcium, nitrogen
answer:

A