阅读下面短文，简要回答问题。

One of the greatest things about growing older is that you get to stay up late. It’s not just your parents who that decision. Your body lets you enjoy dark hours, too.

Resent study has shown that brain changes during teen years make it easier for kids to stay up late. “But it doesn’t mean that you should stay up late just because you can stay up late,” scientists say. Young people who don’t get enough sleep are often late for school, or they miss it completely. And their grades go down. “If you’re sleeping in school, you’re not learning,” says Mary Carskadon who is a sleep researcher.

Lack of sleep is a growing problem in the United States. Schools have been starting earlier in recent years. And with TV, computers, and video games attracting them, people of all ages are sleeping less than their parents or their grandparents did.

Sleep is important because it gives our bodies time to recover from the stress (压力) of living. Studies show that the adults (成人) who sleep less than 6 hours a night have mote heart problems and die sooner than the adults who sleep 7 to 8 hours a night.

How much sleep do you need? It depends mainly on your age. Babies often sleep for the most of the day. By the time they’re 10 years old, kids need an average of 10 hours a night. As they get older, kids have signs to sleep less. But given the chance in an experiment to sleep as long as they want to, young teenagers have 10 hours of sleep. There are even some indications that teenagers may need more sleep than younger kids.

1. Find in the passage a word closest in meaning to the underlined word “indications”.（在文章中找一个与indications意义相近的词） (2分)

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2. What is the main cause of young teenagers’ staying up late? (回答字数不超过8个) (3分)

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3. Why is sleep so important? (回答字数不超过13个) (3分)

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4. What can be the best way to ensure the sleeping time of the school children in the USA according to the passage? (回答字数不超过6个) (2分)

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