the amplifier the battery the microphone the speaker
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: 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?
Possibilities:
- the amplifier
- the battery
- the microphone
- the speaker

the microphone