The college entrance examination is just around the corner. Homework and tests will keep many of you up late at night, and you may plan to make up for your lost sleep during the weekends. {#blank#}1{#/blank#} is it useful? A study published in the journal Current Biology completely has changed {#blank#}2{#/blank#} people used to think. It shows that the habit of sleeping in on weekends doesn't fix the damage done by a lack of sleep during the week. Even {#blank#}3{#/blank#} (bad), it may damage your health.

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With the completion of the Human Genome（基因组）Project more than 20 years ago, and the discovery of the double helix structure of DNA enjoying its 70th birthday last year, you might assume that we know how life works. Think again!

Evolution has a 4bn-year head start on us. However, several aspects of the standard picture of how life works-the idea of the genome as a blueprint, of genes as instructions for building an organism, of proteins as precisely tailored molecular（分子）machines and more-have wildly reduced the complexity of life. 

In the excellent book How Life Works, Philip Ball explorers the new biology, revealing life to be a far richer, more delicate affair than we have understood. Ball explains that life is a system of many levels-genes, proteins, cells, tissues, and body modules-each with its own rules and principles, so there is no unique place to look for an answer to it. 

Also, How Life Works is a much more appealing title than the overused question of "What is life?". We should be less concerned with what a thing is, and rather more focused on what a thing does. Defining a living thing implies an unchangeable ideal type, but this will run counter to the Darwinian principle that living things are four-dimensional, ever changing in time as well as space.

But it's an idea that is deeply rooted within our culture. Ball points out that we rely on metaphors（比喻）to explain and explore the complexities of life, but none suffice. We are taught that cells are machines, though no machine we have invented behaves like the simplest cell; that DNA is a code or a blueprint, though it is neither; that the brain is a computer, though no computer behaves like a brain at all.

Ball is a terrific writer, pumping out books on incredibly diverse subjects. There's a wealth of well-researched information in here, and some details that are a bit chewy for the lay reader. But the book serves as an essential introduction on our never-ending quest to understand life.

Earlier this year Rodney Smith Jr. made headlines when he drove eight hours from his home in Huntsville. Alabama, to cut the lawn for an elderly soldier in North Carolina who couldn't find anyone to help him with his yard work.

That wasn't the first time the twenty-nine-year-old Bermuda native had gained such attention. To do his good deeds, Rodney often finds leads for those in need through social media.

Back to one August afternoon in 2015, Rodney Smith Jr. was driving home. That's when Rodney saw an elderly man struggling to mow his lawn. He would take a couple of shaky steps, using the handle to stabilize himself, pause, then slowly push the mower again. Rodney decided to help. Mr. Brown thanked him greatly, and Rodney went home feeling satisfied.

Sitting at his computer to do his homework, Rodney couldn't get Mr. Brown out of his mind. There must be many Mr. Browns out there. He went online and posted that he would mow lawns for free for senior citizens. Messages flooded in.

One day a cancer-battling woman said she wasn't having a good day. Rodney decided to do more than mowing lawns. After he finished mowing, he knocked on her door. "You're going to win this fight, Madam", he said. Then he asked folks to pray for her on social media.

Word of Rodney's mission spread. A grandmother in Ohio said he'd encouraged her 12-year-old grandson to mow lawns. He got a letter from a seven-year-old boy in Kansas. "Mr. Rodney, I would like to be a part of your program, and I'll make you proud," he wrote.

That gave Rodney an idea. In 2017, he decided to establish a programme Raising Men Lawn Care Service to make a national movement for young people. The kids learn the joy of giving back.

Yard work seems like a small, simple thing, but taking care of the lawn means a lot to the people they do it for. "When we mow their yards for free, they can use the money for healthcare and food etc. It means more than you would think," Rodney said.

One teacher had two students. One of them had a positive vision while the other had the 1 one.

One day, the teacher 2 for a park with both the students and while wandering in the garden, they 3 a mango tree from which some ripe and juicy mangoes were 4 . On seeing this, the teacher thought to 5 both of his students. Then, he asked the first one, "My dear child, what do you think of this mango tree?"

The student answered instantly, "Teacher, in spite of people 6 this tree with stones, it gives us sweet and juicy mangoes. It does 7 but still it gives us fruits. I wish all human beings learn this important 8 from the mango tree-to share their 9 even if they have to suffer for this."

After that, the teacher asked the other student the same question. The student 10 answered, "Teacher, this mango tree is no good and will not give mangoes by itself but only when we hit it with stones and 11 . Therefore, we should hit it hard to get sweet mangoes from it. That is the only way to 12 these mangoes. It is also clear from this tree that in order to get good 13 from others, we need to be violent and only when we become violent, then and only then will we get 14 ."

The teacher was delighted with the answer given by the first student because he had an admirable vision and 15 the tree with positive vision.