单选题：The average young American now spends practically every waki

The average young American now spends practically every waking minute—except for the time in school，though reluctantly—using a smart phone, computer, television or other electronic devices, according to a new study.
Those ages 8 to 18 spend seven and a half hours a day with such devices, compared with less than six and a half hours five years ago. And that does not count the hour and a half that youths spend texting，or the half hour they talk on their cellphones. And because so many of them are multitasking—say, surfing the Internet while listening to music—they pack on average nearly 11 hours of media content into that seven and a half hours.
The study's findings shocked its authors, who had concluded in 2005 that use could not possibly grow further, and confirmed the fears of many parents whose children are constantly tethered to media devices. ① It found, moreover, that heavy media use is associated with several negatives, including behavior problems and lower grades.
Dr. Michael Rich, a pediatrician at Children's Hospital Boston who directs the Center on Media and Child Health, said that with media use so ubiquitous, it was time to stop arguing over whether it was good or bad and accept it as part of children's environment, “like the air they breathe, the water they drink and the food they
eat.”
Contrary to popular wisdom, the heaviest media users reported spending a similar amount of time exercising as the light media users. Nonetheless, other studies have established a link between screen time and obesity.
While most of the young people in the study got good grades, 47 percent of the heaviest media users—those who consumed at least 16 hours a day—had mostly C's or lower, compared with 23 percent of those who typically consumed media three hours a day or less. The heaviest media users were also more likely than the lightest users to report that they were bored or sad, or that they got into trouble, did not get along well with their parents and were not happy at school. The study could not say whether the media use causes problems, or, rather, whether troubled youths turn to heavy media use.
“This is a stunner,”said Donald F. Roberts, one of the authors of the study. “In the second report, I remember writing a paragraph saying we've hit a ceiling on media use, since there just aren't enough hours in the day to increase the time children spend on media. ② But now it's up an hour. ”
阅读以上文章，回答题It can be inferred that young Americans probably __________． A．are not allowed to use electronic devices in schoo
B． prefer a smart phone to a computer or televisio
C． want to buy the newest electronic device
D． are all very good at sending textin