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.

In an accurate diagram of the solar system, which object would be shown closest to Earth?  
 (A) the Moon (B) the asteroid belt (C) Mars (D) Saturn
A

A hearing aid is a small device that contains an amplifier, a battery, a microphone, and a speaker. Which part of a hearing aid functions to detect sounds in the user's environment?  
 (A) the amplifier (B) the battery (C) the microphone (D) the speaker
C

A scientist designs a mathematical model of the rock cycle. The model predicts how changes in Earth processes will affect the amounts of different types of rock on Earth. Which quantity should stay the same as Earth processes change?  
 (A) the average rate at which Earth rotates (B) the average distance of Earth from the Sun (C) the total number of inactive volcanoes on Earth (D) the total amount of material on Earth

D