Ellen Sims is an 18-year-old college student．She has an important history exam tomorrow morning．Ellen is going to study all night．She is not going to sleep at all．Many college students，like Ellen，do this often．They think that they can study all night．And they think that in the morning，they will remember everything that they studied the night before，Ellen thinks that this is a good way to study，but many doctors disagree．They say that sleep is very important for memory and brain development．

Scientists at Harvard Medical School in the US studied sleep and memory．They studied 24people．First，they asked the people to look at a picture and remember it．At night，they put the people in two groups of 12．Group One went to sleep．Group Two did not．A few days later，the scientists showed some pictures to both groups．They asked the people to find the picture they saw before．The people in Group One did well．But the people in Group Two did not do well．It wasn't easy for them to remember the picture．What happened？Scientists say that sleep helps our memory．After we learn something new，sleep helps us remember it．And when we don't sleep，we can forget new things．

Scientists say that many teenagers，like Ellen，sleep too little．They go to school and they work，too．They also spend time with their friends．They are always busy and they think that sleep doesn't matter．But scientists say the brains of teenagers are still developing，and sleep is a very important part of the development．When teens sleep less than six hours，they can't think clearly．That is not very helpful for a student who is taking an exam．

65．Is Ellen going to study all night before the history exam？___

66．Who studied sleep and memory？___

67．How many people were there in each group for this study？___

68．Why did Group One remember the picture better？___

69．What can we learn from the passage？___．