Q: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 to ," Josef Shargorodsky of Brigham and Women's Hospital in Boston told Reuters. "Often people won't notice it, but even very little hearing loss may influence 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 influence 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 know from before that it is difficult to ask this age group about noise exposure - _ " 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. Which of the following is true according to the passage? A) Hearing loss may lead to slow language development. B) Hearing loss in old people is as common as in young people. C) Researchers have already found some causes of hearing loss. D) Teenagers know MP3 is harmful, but they can't stop listening to it.
A:
A