题目内容：

In today’s world， sleep experts say that for a better night’s rest， Americans should turn off their smartphones or iPad before sleeping. Such electronic products make the brain more active， and then influence their sleep. But according to a latest survey， more than 90% of Americans regularly use a computer or some other kinds of electronic products in the hour before bed.

Researchers are finding that man-made light from some electronic products at night may reduce the brain chemicals(化学物质) that help sleep. The researchers showed that sitting in the light from computer tablets clearly lowered levels of the chemical which manages our body clocks and plays a role in the sleep cycle.

In the study， the researchers let volunteers read， play games and watch movies on a tablet for different time while measuring(测量) how much light their eyes received. They found that two hours of sitting before a bright tablet screen at night reduced the sleep chemical levels by about 22%.

Studies of students using computers at night have got the similar results. And researchers say that may not only cause sleeplessness， but also raise the risk of obesity(肥胖症)， diabetes(糖尿病) and other diseases.

To be on the safe side， the researchers advise us to use computers less before bed， or at the very least turning down your screen as much as possible.

根据材料内容选择最佳答案。

1.What can we learn from the first paragraph?

A. Americans don’t get enough sleep.  

B. Electronic products are very popular.

C. The brain becomes more active at night. 

D. Sleep experts never use smartphones.

2.The volunteers in the study did the following things EXCEPT ___________.

A. listening to music     

B. playing computer games

C. watching movies    

D. reading electronic books

3.How may electronic products influence people’s sleep?

A. Make our brains more active. 

B. Make our body weak.

C. Lower our brains’ chemicals that help sleep.

D. Change our body clocks.

4.The underlined word ＂that＂ probably means ___________ in the passage.

A. making a survey about sleep   

B. using smartphones in the daytime

C. sitting in a bright room    

D. surfing the Internet at night

5.What does the passage tell us to do to have a good sleep?

A. Learn to use smartphones or iPad. 

B. Watch some relaxing TV programs.

C. Turn down the screen to the lowest.

D. Try to sleep earlier than before.