(D)
About 16 million people in the United States have lost some of their hearing. About two million others are extremely or completely deaf. They cannot hear speech or most other sounds in their everyday life, even with a hearing aid to make sounds louder.
There are several kinds of hearing loss. The first kind results from disease or injury to the outer or middle part of the ear. The damage prs sound waves from reaching the inner ear. Usually, this form of hearing loss is not extreme. And a hearing aid or medical treatment can often restore hearing. A second kind of hearing loss involves the nerves (神经). It is caused by damage to the inner ear. A loud noise or disease may destroy some of the tiny nerve cells that carry sound. People suffering this kind of damage may lose the ability to hear some sounds, high or low. The third kind of deafness is called a central hearing loss. It is caused by damage to the hearing nerves leading to the brain or in the brain itself.
Deafness is the most common bodily disability (残疾) in America. Often nothing can be done to stop it. But many cases can be pred. One thing is responsible for most hearing loss. That one thing is noise. Telephone bells, loud music, machines. In industrial countries, especially, these things make the world very noisy. Studies have shown that old men in quiet African villages have much better hearing than young people in America. Other sources of deafness. include accidents, drugs and illnesses. (D)Hearing loss caused by damage to ______ can often be restored.