A

Cellphones,tablets,and computers are keeping children and teenagers awake at night-even

when they're not in use,according to new research.A study published on Monday in JAMA Pediatrics says that media devices are causing kids to sleep less and reducing the quality of sleep that they get.This leads to trouble of staying awake the next day.

 Researchers analyzed hundreds of studies of children and teens aged 6-19.The scientists found a strong and consistent association between the use of technology at bedtime and pool sleeping.The reason is not just that kids are staying up too late with their devices.Using a computer can overstimulate the mind and emotions,the researchers say.A smartphone or tablet also gives off a light that affects the body's natural timing.These factors contribute to poor quality sleep.And many kids could be at risk.According to the study,72%of all children and 89% of adolescents have at least one device in their sleep environment.Most of these devices are used near bedtime.

£¢The harmful association between screen-based devices and kids' sleep is a major public health concern,"the study concludes.In their conclusion,the researchers urge parents to understand the damaging influence of device use before sleep.

21.What do the researchers disagree with?

A.Children even in dreams can be influenced by media devices.

B.Most adolescents like to play media devices before sleep.

C.Using media devices on bed makes kids sleep difficultly.

D.Using media devices cannot excite the mind and emotions.

22.How does a smartphone affect a child's sleep?

A.By making noises.                                   B.By giving off a light.

C.By attracting a kid's attention.                 D.By sending out electronic waves.

23.What can we learn from the second paragraph?

A.Media devices anytime put kids in danger.

B.Adolescents are more easily affected than children by phones.

C.Using technology at bedtime causes poor sleeping.

D.Media devices affect kid's performance at school.