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]: When pressure is released along a fault line, the energy produced spreads as mechanical waves in the form of an earthquake. The mechanical waves transferred to the air become  
 (A) sound. (B) electricity. (C) light. (D) heat.
[A]: A


[Q]: 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
[A]: C


[Q]: Biotic nitrogen fixation is performed by certain  
 (A) lichens. (B) viruses. (C) bacteria. (D) mammals.
[A]:
C