阅读下列短文，从每题所给的A、B、C、D四个选项中选出最佳选项。
A
A hearing aid is an electronic device that can receive and amplify（（放大)incoming soundsfor people with hearing impairment（损伤) to aim for better sound understanding throughproper amplification.
Here's how they work :
●A microphone picks up sound around you.
●An amplifier makes the sound louder.
●A receiver sends these amplified sounds into your ear.
Not everyone with hearing loss can benefit from hearing aids—only 1 in 5 people couldhave improvement to wear them. Most of the time, they're for people who have damage totheir inner car or the nerve that 1inks the ear with the brain.
What can I expect from my hearing aids?
Unlike eyeglasses,hearing aids do not correct your hearing back to normal. Instead,hearing aids function to amplify sounds in a particular range of pitches—the range where thehearing loss exists,Included in those sounds are speech or environmental sounds such as bellsringing,birds singing, conversations from nearby tables at a restaurant or busy traffic noise.
While the hearing aid technology today is excellent, the devices are still an“aid”andcannot separate the desired speech signal from the background noise as well as our brain andtwo normal functioning ears can, Therefore,it is important to employ communicationstrategies when using hearing aids in difficult listening environments.
Do I need one or two hearing aids?
If hearing loss exists in both ears, there is greater benefit in using a device in each ear—similar to wearing eyeglasses with two lenses.There are always exceptions to the general ruleand that will be discussed with your audiologist（听觉矫正专家).
21. What is the primary function of a hearing aid?
A.To diagnose hearing loss.
B.To repair damage to the inner ear.
C.To protect the ears from loud noises.
D.To pick up and amplify incoming sounds.
22.Which best describes the hearing aids today?
A.They are imperfect. B.They are cost-effective.
C.They are unreliable. D.They are user-friendly.
23. What does the last part of the text intend to do?
A.To present a basic fact. B.To clarify an exception.
C.To make a suggestion. D.To explain a general rule.
