A、Declining health. B、Lack of attention. C、Loss of motivation. D、Improper behavior. B

Reducing the amount of sleep students get at night has a direct impact on their performance at school during the day. According to classroom teachers, elementary and middle school students who stay up late exhibit more learning and attention problems. This has been shown by Brown Medical School and Bradley Hospital research.
    In the study, teachers were not told the amount of sleep students received when completing weekly performance reports, yet they rated the students who had received eight hours or less as having the most trouble recalling old material, learning new lessons and completing high-quality work.
    Teachers also reported that these students had more difficulty paying attention. The experiment is the first to ask teachers to report on the effects of sleep deficiency in children. Just staying up late can cause increased academic difficulty and attention problems for otherwise healthy, well-functioning kids, said Garharn Forlone, the study’s lead author. So the results provide professionals and parents with a clear message: when a child is having learning and attention problems, the issue of sleep has to be taken into consideration. "If we don’t ask about sleep, and try to improve sleep patterns in kids’ struggling academically, then we aren’t doing our job," Forlone said. For parents, he said, the message is simple, "getting kids to bed on time is as important as getting them to school on time."
Questions 16 to 18 are based on the passage you have just heard.
16. What were teachers told to do in the experiment?
17. According to the experiment, what problem can insufficient sleep cause in students?
18. What message did the researcher intend to convey to parents?