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]: What force pulls things towards the center of Earth?  
 (A) magnetism (B) gravity (C) friction (D) energy
[A]: B


[Q]: One role of a producer in a food chain is to provide  
 (A) water for plants (B) sunlight for plants (C) nutrients for animals (D) shelter for animals
[A]: C


[Q]: When athletes begin to exercise, their heart rates and respiration rates increase. At what level of organization does the human body coordinate these functions?  
 (A) at the tissue level (B) at the organ level (C) at the system level (D) at the cellular level
[A]:
C