21．Why would human beings waste a third of their lives sleeping when they could be doing more important things like looking after their families or working？Some scientists believe sleeping helps recharge the body.while others think it is important for strengthening newly formed memories.Now，there is new evidence which suggests that the purpose of sleep may be to forget some of the millions of new things we learn each day.
The neurons in the human brain consist of fibers called dendrites （樹突）.These grow as we learn new things and connect the brain's cells to each other at contact points called synapses （突觸）.The larger the dendrites become and the more cells they connect，the more information we store.
In 2018.Giulio Tononi and Chiara Cirelli，both biologists at the University of Wisconsin Madison，suggested a new idea：The things our brains learn each day result in so many synapses that things start to get a little messy.Sleeping allows us to sort through （整理） the "noise" and
dispense all the unnecessary information.leaving behind only the most important memories.
Recently，the university's research has provided direct evidence to support the theory.The experiment involved analyzing 6.920 synapses in the brain shavings from two groups of mice over a four-year period：one group had been allowed to sleep，while the other had been kept awake and entertained with toys.The researchers discovered that the brain shavings of the sleeping mice had nearly 20 percent fewer synapses than those that had been kept awake and entertained.
It was also evident during the study that the brain does not shave every synapse.20% of neurons remained unchanged：these were most likely well established memories.Therefore.although we may be sleeping to forget some of what we've learned，the brain "forgets" in a smart way.
Most researchers believe clearing our brains is not the only purpose of sleep.
Resting our minds and bodies has also been found to help with other biological functions like strengthening our immunity.Though scientists may never agree on a single reason.they are all sure of one thing — a good night's rest is essential for our health.So try and spend at least a third of your day sleeping!
（1）What's the purpose of sleeping according to the new discovery？（no more than 15 words）
（2）What's the main idea of Paragraph 2？（no more than 10 words）
（3）What does the underlined word "dispense" in Paragraph 3 probably mean？（no more than 5 words）
（4）What agreement do all the scientists probably reach about sleeping according to the text？（no more than 10 words）
（5）Do you think a good night's sleep will benefit your next-day study？Please explain in your own words. （no more than 20 words）
