A new Northwestern University study reaffirms the importance of getting a good night's sleep.By examining fruit flies' brain activity and behavior，the researchers found that deep sleep has the power to clear waste from the brain.This waste potentially includes poisonous proteins that may lead to neurodegenerative （神經(jīng)退化） diseases. "Waste clearance could be important，in general，for maintaining brain health or for preventing neurodegenerative diseases，" said Dr.Allada，senior author of the study. "Waste clearance may occur during wake and sleep but is greatly strengthened during deep sleep."
Although fruit flies seem very different from humans，the neurons （神經(jīng)元） that govern flies' sleep-wake cycles are strikingly similar to our own.For this reason，fruit flies have become a well-studied model organism for sleep and neurodegenerative diseases.
In this current study，Allada and his team examined Proboscis （針狀喙） Extension Sleep，a deep-sleep stage in fruit flies，which is similar to deep，slow-wave sleep in humans.The researchers discovered that，during this stage fruit flies repeatedly extend and move back their proboscises "This kind of movement moves fluids possibly to the fly version of kidneys（腎），" Allada said. "Our study shows that
this promotes waste clearance and aids in injury recovery."
When Allada's team disturbed flies' deep sleep，the flies were less able to clear the waste from their systems and were more likely to be influenced by injuries.
Allada said this study brings us closer to understanding the mystery of why all organisms need sleep.All animals，especially those in the wild，are incredibly weak when they sleep，but research increasingly shows that the benefits of sleep，including crucial waste removal，are greater than this increased weakness.
（1）How did the researchers draw the conclusion of their study？
C
C
A．By working out the result by chance.
B．By predicting the result from the old data.
C．By making observation and analysis.
D．By making a range of comparisons.
（2）What does the underlined word "this" in paragraph 3 probably refer to？
C
C
A．The disturbance of fruit flies' deep sleep.
B．The governing of fruit flies' sleep-wake cycles.
C．The moving of fluids to the fruit flies' kidneys.
D．The extension and moving of fruit flies' proboscises.
（3）What is mainly talked about in the last paragraph？
D
D
A．The fact that all organisms need sleep.
B．The application of the result of the study.
C．The disadvantages of the sleep of animals.
D．The great value of mankind's and animals' sleep.
（4）Which of the following is a suitable title for the text？
B
B
A．Studies on Proboscis Extension Sleep
B．Deep Sleep Takes Out the Brain Trash
C．Different Functions of Waste Clearance
D．Similarities of Sleep-Wake Cycles Between Fruit Flies and Humans
