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: Which system of the human body provides protection to most of the major organs?  
 (A) skeletal system (B) circulatory system (C) respiratory system (D) muscular system

SOLUTION: A

PROBLEM: Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?  
 (A) miles (B) meters (C) light years (D) astronomical units

SOLUTION: C

PROBLEM: Automobile engines built today are designed to be gas efficient. Gas-efficient engines most likely affect a city by reducing  
 (A) air pollution. (B) heat pollution. (C) noise pollution. (D) light pollution.

SOLUTION:
A