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:
Which of the following statements best explains how the decomposition of plant and animal matter helps to form rich soils?  
 (A) Decomposition adds silt to soil. (B) Decomposition adds water to soil. (C) Decomposition adds oxygen to soil. (D) Decomposition adds nutrients to soil.
answer:
D


question:
Use of nuclear fuel would most likely reduce human contributions to which environmental problem?  
 (A) ozone thinning (B) landfill creation (C) shoreline erosion (D) greenhouse heating
answer:
D


question:
Don throws a ball in the air. The ball comes back to the ground because  
 (A) the wind pushes on the ball with friction. (B) the mass of Earth creates a pull of gravity on the ball. (C) the core of Earth pulls on the ball with a magnetic attraction. (D) the weight of the atmosphere pushes down on the ball.
answer:

B