There is a discovery that students who rely on working at night to improve their grades might want to sleep on that strategy: a new survey in the US says those who never study all night have slightly higher grades than those who do.  A survey of 120 students at St. Lawrence University found that students who have never pulled an all-nighter on average have higher grades than those who have. The survey found those who did not study through the night had a grade point average of 3.2 compared to 2.95 for those who have.  The study, by assistant professor of psychology Pamela Thacher, is to be included in the January issue of Behavioral Sleep Medicine. "It's not a big difference, but it's pretty striking," Thacher said. "I am primarily a sleep researcher and I know nobody thinks clearly at 4 in the morning. You think you do, but you can't."  Many college students, of course, have inadequate or irregular sleep, for reasons ranging from excessive caffeine to poor time management.  "A lot of students were under the impression that all-nighters were a very useful tool for accomplishing work, that caffeine intake was very useful in meeting deadlines and stuff like that," said Chatani, who had a 3.4 grade point average last term.  Dr Howard Weiss, a physician at St. Peter's Sleep Center in Albany, said the study results make sense.  "Certainly that data is out there showing that short sleep duration  ly interferes with concentration, interferes with performance on objective testing," he said.  Some night owls  do get good grades, of course, which may be explained by circadian rhythms , Weiss said. Some people have different 24-hour body clocks than others, and may do better depending on class and testing times, Weiss said. The purpose of the passage is to tell us   _  .
the bad effects of pulling an all-nighter pulling an all-nighter leads to sleep problems Thacher' s doubt about all-nighters all-nighters hurt students' grades
Question: There is a discovery that students who rely on working at night to improve their grades might want to sleep on that strategy: a new survey in the US says those who never study all night have slightly higher grades than those who do.  A survey of 120 students at St. Lawrence University found that students who have never pulled an all-nighter on average have higher grades than those who have. The survey found those who did not study through the night had a grade point average of 3.2 compared to 2.95 for those who have.  The study, by assistant professor of psychology Pamela Thacher, is to be included in the January issue of Behavioral Sleep Medicine. "It's not a big difference, but it's pretty striking," Thacher said. "I am primarily a sleep researcher and I know nobody thinks clearly at 4 in the morning. You think you do, but you can't."  Many college students, of course, have inadequate or irregular sleep, for reasons ranging from excessive caffeine to poor time management.  "A lot of students were under the impression that all-nighters were a very useful tool for accomplishing work, that caffeine intake was very useful in meeting deadlines and stuff like that," said Chatani, who had a 3.4 grade point average last term.  Dr Howard Weiss, a physician at St. Peter's Sleep Center in Albany, said the study results make sense.  "Certainly that data is out there showing that short sleep duration  ly interferes with concentration, interferes with performance on objective testing," he said.  Some night owls  do get good grades, of course, which may be explained by circadian rhythms , Weiss said. Some people have different 24-hour body clocks than others, and may do better depending on class and testing times, Weiss said. The purpose of the passage is to tell us   _  .
A. the bad effects of pulling an all-nighter
B. pulling an all-nighter leads to sleep problems
C. Thacher' s doubt about all-nighters
D. all-nighters hurt students' grades
Answer: