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:
Compost piles have many parts, such as leaves, moisture, vegetables, and microorganisms. Which part of a compost pile breaks down materials and adds nutrients to the soil?  
 (A) leaves (B) moisture (C) vegetables (D) microorganisms
answer:
D


question:
Air is composed of many different substances. Which of the following components of air is a compound rather than an element?  
 (A) Argon, Ar (B) Oxygen, O2 (C) Water, H2O (D) Nitrogen, N2
answer:
C


question:
Soil will pack down over time which decreases the ability of the soil to hold water. Which animals would best help the soil hold water?  
 (A) earthworms making tunnels under the surface (B) cattle making depressions with their hooves (C) horses making trenches when they gallop (D) sheep pulling up plants by their roots
answer:

A