As many as one in five US teenagers have some degree of hearing loss, according to researchers.
They say the problem is growing.
Teenagers really don’t pay attention to how much noise they are exposed (暴露) to, Josef Shargorodsky of Brigham and Women’s Hospital in Boston told Reuters. “Often people won’t notice it, but even slight hearing loss may affect language development,” said Shargorodsky, one of the researchers.
The study compared surveys from the early 1990s and the mid-2000s. Each included a few thousand teenagers. In the first survey, about 15 percent of teenagers had some degree of hearing loss. Some 15 years later, that number had risen by a third, to nearly 20 percent.
“This certainly is big news,” said Alison Grimes, an ear doctor. Hearing loss is very common in old people, Grimes said, but she added that it was worrying to see it happen in the younger age group.
In babies and young children, hearing problems are known to slow language development. The science is less clear for teenagers, but it is easy to imagine how being hard of hearing could affect learning, said Grimes,.
The reasons for the rise are still unclear. When researchers asked teenagers about noise exposure – on the job, at school or from activities, for example – the teenagers didn’t report any change. But Shargorodsky said that might not be true. “We knew from before that it is difficult to ask this age group about noise exposure – they underestimate (低估) it.” Few people would call it noise when they listen to music on their MP3 player, for example. “There is a difference between what we think is loud and what is harmful to the ear,” said Grimes.
Although it’s not clear that the MP3 players cause teenagers’ hearing loss, Grimes said it was still a good idea to turn down the sound and take short breaks from listening.
According to the researchers, in a US class of 40 students, about ____ students have some degree of hearing loss.

A．one

B．five

C．six

D．eight

Which of the following statements is true according to the article?

A．Slight hearing loss does not influence learning.

B．Only a few old people have hearing problems.

C．Hearing problems can slow language development.

D．Noise exposure is clearly noticed by teenagers.

About hearing loss, it can be inferred that ________.

A．the reasons for the rise have been found	B．MP3 players are to blame
C．listening to loud music may be a cause	D．noise is the main reason

The article was written to ______.

A．warn teenagers that loud music might be harmful

B．explain what kinds of noises might affect studies

C．suggest that teenagers shouldn’t listen to loud music

D．show how important hearing can be for learning