TASK DEFINITION: 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.
PROBLEM: 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

SOLUTION: D

PROBLEM: Which property of proteins best allows them to perform an enormously diverse range of functions?  
 (A) their large, chemical-energy reserve (B) their large, stored-electric potential (C) the complexity of their folded structure (D) the wide variety of elements they include

SOLUTION: C

PROBLEM: Which of these best explains why peer review is critical to the advancement of science?  
 (A) It provides an independent assessment of conclusions. (B) It allows laboratories to practice science. (C) It creates more job opportunities for scientists. (D) It ensures all scientists will study similar phenomena.

SOLUTION:
A