ABrownUniversitysleepresearcherhassomeadviceforpeoplewhorunhighschools：Don'tstartclassessoearlyinthemorning．Itmaynotbethatthestudentswhonodoffattheirdesksarelazy．Anditmaynotbethattheirparentshavefailed

　　A Brown University sleep researcher has some advice for people who run high schools：Don't start classes so early in the morning．It may not be that the students whonodoff at their desks are lazy．And it may not be that their parents have failed to enforce（确保） bedtime．Instead，it may be that biologically（生物学上） these sleepyhead（瞌睡虫）students aren't used to the early hour．

　　"Maybe these kids are being asked to rise at the wrong time for their bodies，"says Mary Carskadon，a professor looking at problem of adolescent （青春期的）sleep at Brown's School of Medicine．

　　Carskadon is trying to understand more about the effects of early school time in adolescents．And，at a more basic level，she and her team are trying to learn more about how the biological changes of adolescence affect sleep needs and patterns（方式）．

　　Carskadon says her work suggests that adolescents may need more sleep than they did at childhood，no less，as commonly thought．

　　Sleep patterns change during adolescence，as any parent of an adolescent can prove．Most adolescents prefer to stay up later at night and sleep later in the morning．But it's not just a matter of choice---their bodies are going through a change of sleep patterns．

　　All of this makes the transfer（迁移）from middle school to high school---which may start one hour earlier in the morning-all the more difficult，Carskadon says．With their increased need for sleep and their biological clocks set on the"sleep late，rise late"pattern，adolescents are up against difficulties when they try to be up by 5or 6a．m．for a 7：30a．m．first bell．A short sleep on a desktop may be their body's way of saying．"I need a timeout．"

　　34．Carskadon suggests that high schools should not start classes so early in the morning because

　　___．

　　A．it is really tough for parents to enforce bedtime

　　B．it is biologically difficult for students to rise early

　　C．students work so late at night t