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.
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Question: When the cardboard cone of a radio speaker vibrates, it produces a sound in the air around it. The cone produces this sound by transferring which of the following to the air around it?  
 (A) heat (B) current (C) wave motion (D) magnetic force

Answer: C


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: Ana rolled her wagon down the ramp to reach the playground. There, she and her sister played on the seesaw. Which set of simple machines has Ana used?  
 (A) Lever, pulley, and wedge (B) Pulley, inclined plane, and screw (C) Wedge, wheel and axle, and screw (D) Wheel and axle, inclined plane, and lever

Answer:
D