A、iPods, CD players and Walkman. B、CD players, radio and laptop computers. C、Radio, Walkman and laptop computers. D、CD players,

Electronic devices are changing the way people listen to music. But studies show the devices may be causing hearing loss in my people. Some experts say people may be playing them too loud and for too long.
Researchers from Zogby International did a study for the American Speech-Langusge-Hearing Association. It involved 300 high school students and 1,000 adults. They were asked about their use of portable music devices. Some of the most popular are Apple Computer’s iPud, C.D. players and portable laptop computers. 40 percent of students and adults said they set the sound levels, or volume, at high on their iPods. But students were two times more likely to play the music at a very loud volume. More than half of the students said they would probably not limit their listening time. And about a third said they were not likely to reduce the volume.
The study found that more than half of the students and less than 40 percent of the adults had at least one kind of hearing loss. Heating experts say part of the problem is the listening equipment people are using. They say large earphones that cover the whole ear are probably safer than the smaller earplugs that come with most music players. Earplugs are thought to be less effective than earphones in blocking out foreign noises.
Hearing loss may not be apparent for years. But once it happens, it is permanent. About 30 million Americans have some hearing loss. One third of them lost their heating as a result of loud noises.
How can listening equipment cause hearing loss in people?

What are the most popular portable music devices mentioned in the study?