阅读下面短文，请从短文后所给各题的4个选项(A、B、C、D)中选出一个最佳选项。

     Sleep has long been a concern of educators. Some schools even send notes to parents reminding them to make sure that their children get enough sleep before examinations. Such concerns and school practices are supported by findings of a recent research, which is conducted by a psychologist named Gahan Fallone at Brown Medical School. According to the research, staying up an hour or two past bedtime makes it far harder for kids to learn.
     Fallone set out to test whether teachers could find out problems with attention and learning when students stayed up late. In his three-week experiment, he studied 74 students aged between 6 and 12. In the first week, the students went to bed, woke up at their usual time and got 9 to 9.5 hours of sleep each night. In the second week, they were given no fewer than 10 hours in bed. In the third week, they were kept up later than usual and got less sleep: 8 hours for first-and second-year students and 6.5 hours for the older children.
     Although they were not told how long the children slept every night during the three-week experiment, the teachers reported that the students had more problems with their learning during the third week. With the help of the teachers' report, Fallone concluded that when students had less than 8 hours of sleep, they were more forgetful; they even had trouble learning new lessons and concentrating. Accordingly, Fallone recommended 10 to 11 hours of sleep a night for children and 8.5 hours for teenagers.