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]: 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
[A]: D


[Q]: Carolina uses a microscope to view a soil sample taken from her backyard. Which part of the soil would she ONLY be able to see with a microscope?  
 (A) bacteria (B) grass (C) rainwater (D) rocks
[A]: A


[Q]: Which situation would most likely cause an object to travel in a circular motion?  
 (A) one force acting on the object in the opposite direction of the motion (B) two forces acting on the object in the same direction as the motion (C) one force acting on the object perpendicular to the direction of the motion (D) two forces acting on the object in different directions to the motion
[A]:
C