Training for a marathon requires careful preparation and steady, gradual increases in the length of the runs. {#blank#}1{#/blank#}, buy the best-fitting, best-built running shoes you can find. No one can say which brand will work best for you or feel best on your feet, so you have to rely on your experience and on the feel of each pair as you shop. When you have found shoes that seem right, walk in them f or a few days to double-check the fit. {#blank#}2{#/blank#}. As always, you should stretch(伸展)at least ten minutes before each run to prevent injuries.

    During the first week, do not think about distance, but run five minutes longer each day. {#blank#}3{#/blank#}, it is wise to take a day off to rest. But during the next week, set a goal of at least a mile and a half per run. {#blank#}4{#/blank#}. After two weeks, start timing yourself. {#blank#}5{#/blank#}. Depending on the kind of race you plan to enter, you can set up a timetable for the remaining weeks before the race.

A. If they still feel good, you can begin running in them  

B. Before you begin your training 

C. After six days

D. For a good marathon runner 

E. Now you are ready to figure out a goal of improving distance and time 

F. Time spent for preparation raises the quality of training 

G. With each day, increase the distance by a half mile

    Our planet is home to about seven billion people. Since the 1990s, population experts have predicted the number would grow to nine billion before it begins to slow down and possibly decrease.

    But a new report predicts the world's population is likely to increase to almost 11 billion by 2100. Based on the most modem statistical tools, the new report makes use of government records and considers expert predictions, including death rates, birthrates and international migration, or people moving across borders. The report says during the rest of this century, Africa's population will grow from about 3.5 billion to 5.1 billion over the next 85 years.

    John is director of the United Nations Population Division. He says that in the past, researchers thought population growth in Africa would be similar to that of other areas. They expected slower growth rates as birth control use became more widespread. But he says those ideas were wrong.

    “The level of contraception use has continued to increase but slowly — more slowly than expected, and birthrate therefore has been falling less rapidly than expected, and the population therefore continues to grow somewhat more rapidly than we expected.

    The new findings are based on a joint research project of the United Nations and the University of Washington,

    The researchers believe the population of Asia will reach five billion by 2050. That is up from the current 4.4 billion. And then begin decline. The researchers also believe that North America, Europe, Latin America and the Caribbean area will have a total population of below one billion.

    John says the pressure of feeding the rising population is likely to be less than that might be expected.

    “The relatively good news is that the world has been winning the race between population growth and food production. If you look back historically over the last 50 years, certainly for the world as a whole and for many, most individual countries and regions, the increase in food production has outpaced the increase of population.”

    As the world around them is changing, teenagers continue to need guidance and support from both parents. Studies show that teens who have an active relationship with their fathers are less likely(可能的)to involve themselves in dangerous behaviors and more likely to succeed in school and develop higher self-worth, because their fathers go beyond social expectations to devote attention to them.

    Peer(同龄人)pressure has always been a big part of the teens' experience. Even the best father can't completely protect their kids from the growing influence of their peer group. However, studies show that teenagers whose fathers focus on their lives are more likely to resist (抵抗)the more bad effects of peer pressure, taking drugs, for example.

    Teens may not like to admit it, but they are watching their parents closely and often follow their example. An interesting finding explains just how important parents are, especially Dad. Swiss researchers discovered that if Dad attends church, even though Mom doesn't, 44 percent of the kids are still more likely to keep going to church as adults. But if Mom goes regularly and Dad never shows up, only 2 percent of the kids continue to attend.

    Teenagers face a lot of difficult choices, especially in their later teens. Fathers don't get to make those choices for them, but they can be influenced. For example, teenagers can learn a lot from their parents' concern on what to do when they finish high school. Should they go directly to college and, if so, where? Should they consider going to trade schools, joining the army or looking for a job? A father's guidance brings a long-term perspective that teens often lack to these important decisions.

    About three decades ago, China was known as the "Bicycle Kingdom". But later on, bikes were replaced by their fuel-powered competitors.

    But recent months have seen a recovery of the humble bike across China, with an increasing number of people choosing cycling instead of driving to schools, to workplaces or to do sightseeing. The introduction of bike-sharing schemes, pioneered by start-ups like Ofo and Mobike, has brought the trend to a new level.

    People can unlock the shared bikes by simply using their smartphone. The bikes are equipped with GPS and can be left anywhere in public for the next user. They're popular among many Chinese people as they provide an effective solution to the "last mile" problem, which refers to the final leg of a person's journey.

    " In places where the subway doesn't extend, where it's difficult to change from one kind of transport to another, it's so easy to get where you want to go with Mobike," Hu Hong,29,told AFP. She pedals(骑车)to her Shanghai real-estate job.

    However, the schemes have also led to problems such as illegal parking, vandalism(故意毁坏) and theft. Last month, two nurses in Beijing were placed under administrative punishment for five days for putting locks on two shared bikes. And in December, a man who stole a shared bike was sentenced to a 3-month detention(拘留),and fined 1 ,000 yuan by the Shanghai Minhang People's Court.

    " Bike-sharing is a greener method of transportation and provides a user-friendly experience,"said Liu Xiaoming, vice-minister of transport.

    " But it's a combination of online and offline business. Operators are usually strong in online services, but lack offline business experience, which causes problems."

    Now, Chinese service operators are trying to solve the problems. For example, a bike- sharing company called Mobike sets a 100-point credit score for each user, with points taken in the case of bad behavior. Once a score drops below 80, bike rental is increased to 100 yuan per 30 minutes, up from 0.5 - 1 yuan.

D

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.