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.

They talk about the straw that broke the camel's back, but really it should be the password that wiped out my memory bank. 

I was going along fine -with instant recall of my bank PIN (密码)，my mobile phone number and the date of my cousin's birthday before I downloaded a gas station payment app for its new customer discount. It asked me to create a password. When I typed in "gas 1", it was rejected for not being complex enough. I tried again: "IHateHearlessOilCompanies@". But that was too long and didn't include "at least one number". But here is the thing: as soon as 1 added the fresh password into my memory, I instantly forgot all the others. My brain had hit its limit for passwords. I now know nothing. 

I had entered some passwords in a notebook. Of course, I didn't write down the actual passwords, in case it fell into the wrong hands. Instead, I masked them in a way that only a family member could figure them out. For example, I combined my bank PIN with our postal code, then added it to a list of phone numbers. It would fool even Albert Einstein.

Maybe we need a system like the one we use to remember people's names. You know, you form an association between a person's characteristics and their name by whispering "Skinny George, Skinny George" in heart after meeting them. The risk is that, upon seeing him, you'll burst out the phrase. "Skinny George" might not mind, but it's possible "Boring Betty" will. As for remembering passwords as you change them, you could simply use the first and last letters of your favorite singer's greatest hits, together with the year of their release.

Maybe I'll try that one out- -but only after describing the system in the notebook. Then I'll hide it in a place so secret that I'll never remember where it is. 

    In my early thirties, I decided to climb Mount Kilimanjaro, the highest mountain in Africa at 5, 895meters above sea level. 

    After months of preparation, I started my great 1 . At the base of the mountain, I met Mik, a local porter, who warmly 2 me. Mik's job was to carry my equipment up the mountain, set up the tent, and carry everything back down after reaching the 3 . 

    The first day of the climb was 4 the rain forest, across a slippery , muddy ground covered with tree roots and vines (藤蔓) . Mik was carrying 30 kilos on his head! By that evening, we made it to 3, 000meters. The air was 5 and it was colder. When I arrived at the campsite for the night, my tent was already set up and waiting for me. 

    Day two was much steeper and rockier. I really had to 6 what I was doing. And I felt guilty for the tough 7 Mik had to work in. Yet when I turned to Mik, he said with the biggest smile, "pole, pole, "which means"8 , take it easy" in his native language. I 9 back, my burden lighter somehow. 

    Over the next five days, the climb got 10 difficult. The temperatures could 11 from 21℃to below freezing in a few hours. At 5, 700 meters, there's only half the oxygen 12 in each breath compared to at sea level. That leaves many people with severe headache. Yet Mik always had a smile and a positive attitude. It had an enormous impact on mo, giving me the 13 to keep going. 

    Even today, when I find myself 14 with anything in life, I just think back to Mik and his smile. A great attitude can bring joy to those around you, or even 15 strangers to the top of a mountain. 

Faye and Matthew Gooding and their five young sons appear to have perfect lives. Mrs. Gooding 1 beautiful photos of life in their four-bedroom house on Instagram(一种社交软件), and more than 32, 000 people 2 them. For the couple themselves, 3 , this "materially(物质地) perfect world" was lacking something—so now they are giving up all their 4 to travel around the world with their kids.

This was the last Christmas that the couple spent in their house, which has already been sold. Most of their belongings are 5 too. Shortly their Ford car will be sold and the family will take just one backpack each.

Mrs. Gooding said: "Some friends and family think Matt and I are 6 to be giving up so much. It's been difficult giving up so many possessions. Yet 7 enjoying spending time with the boys, I found myself cleaning the house all day before. The older ones were at school and I thought, 'I 8 see them'. I admitted how I felt to Matt. He agreed it felt as if our lives moved around 9 things—both of us working to 10 the mortgage(贷款) and keep ourselves in our materially perfect world."

    They will leave this month and plan to start their 11 in Sweden where they have friends.

Mr. Gooding added: "People have said 'aren't you worried about stability and safety?'— 12 as we have five small children. It is a (an) 13 because we are giving up so much. But we can't wait to spend more time with our sons without the 14 of everyday routines. We don't know what will happen, but we do know if we didn't do this we would always 15 it."