Mountaineers have noted that as they climb, for example, up to the 12,633­foot Humphreys Peak in Arizona, plant life changes greatly. In the Sonoran Desert, one climbs into a pine forest at 7,000 feet and a treeless tundra(冻土带) on the top of the mountain. It may seem that plants at a given altitude are associated in what can be called “communities” －groupings of species. The idea is that over time, plants that require particular climate and soil conditions come to live in the same places, and are frequently to be found together. Scientists study the history of plant life and build up a picture of how groups of plants have responded to climate changes and how ecosystems develop. But are these associations, which are real in the present, permanent?

    A great natural experiment took place on this planet between 25,000 and 10,000 years ago, when small changes in the earth's orbit caused great sheets of ice to spread from poles. These glaciers(冰川) covered much of North America and Europe to depths of up to two miles, and then, as the climate warmed, they retreated. During this retreat, they left behind newly uncovered land for living things to occupy, and as those living things moved in they laid down a record we can read now. As the ice retreated and plants started to grow near a lake, they release pollen(花粉). Some would fall into the lake, sink to the bottom and mix with the sand. By drilling into the lake bottom it is possible to read the record of the plant life around the lake. The fossil record seems clear; there is little or no evidence that entire groups of plants moved north together. Things that lived together in the past don't live together now, and things that live together now didn't live together in the past. Each individual living things moved at its own pace. The fossil record seems to be telling us that we should be thinking about preserving species by giving them room to move about－to respond to environmental changes.

    With all the traditional media channels, including newspapers, magazines and television shows, shrinking, advertisers are worrying about how they can reach customers. Banners(横幅) ads on our devices are ugly and disturbing. To overcome various digital problems, the ad industry has been serving up a sneaky(不光明正大的) solution: make ads look less like ads and more like the articles, videos and posts around them.

    This trend, called native advertising, has taken over the Internet; even the websites such as NYTimes.com and Wall-Street.com are using it. On Facebook and Twitter, every 10th item or so is an ad; only the small subtitle “Sponsored（赞助）” appearing in light gray type tells you which posts are ads.

    Won't dressing up ads to make them look like reported articles mislead people? Sometimes, yes. An Interactive Advertising Bureau study found that only 41 percent of general news readers could tell such ads apart from real news stories. And it's getting worse. Advertisers worry that the “Sponsored” label discourages readers from clicking, so some websites are making the labels smaller and less noticeable. Sometimes the labels disappear entirely.

    At a recent talk about the difficulty of advertising in the new, small-screen world, I heard an ad manager tell an impressive story. She had gotten a musical performance – paid for by her soft drink client- perfectly inserted（插入）into a TV awards show, without any moment of blackness before or after. “It looked just like part of the real broadcast!” she recounted happily.

    Look, it is great that native advertising works. But if advertisers truly believe in their material, they should have no problem labeling it as advertising.

    For now native ads continue to be a fashion- with no laws governing them and no labeling standard. But that could change; the Federal Trade Commission has begun considering regulation. If the new generation of digital advertisers clean up their act according to the regulation, native ads might become more acceptable.

    Many automobile makers present their newest designs at car shows around the world. Many designers seek to create the car of the future. One device that is popular among car manufacturers(生产商) is an autopilot. Autopilot permits a car to drive itself without human control.

    A recent car show in Geneva, Switzerland also presented other possible designs, including cars manufactured in 3-D printers.

    Rinspeed is a Swiss design company. It showed a vehicle based on the US electric car Tesla Model S, but the Rinspeed car includes a large television and an espresso coffee maker.

    Frank Rinderknecht is the CEO of Rinspeed. He says he does not want to just sit and watch the steering wheel(方向盘) turn as he rides in a car with autopilot.

    "I want to ride; I want to sleep, relax, watch movies, news, anything else. So that's the vision which we have. One day on the boring motorway traffic, you just do anything which makes your life better," said Rinderknecht.

    One of the most interesting ideas presented at the show is a car built on a 3-D printer. The German engineering firm EDAG designed the car. The body of the vehicle called "Genesis" is printed in one piece from a material called thermoplastic(热塑性塑料).

    Christoph Horvath is spokesman for EDAG.

    "To create a car without the use of any tool. This would be a real revolution for the industry," said Horvath.

    EDAG says it based its design on a turtle shell. The company says the design provides the right amount of strength and firmness.

    Other automakers did not look so far into the future. Czech automaker Skoda presented its "Vision C" model vehicle. The car has an environmentally friendly natural gas engine.

    Jo Davidson is a company spokeswoman. She says the car releases very low levels of the pollutant gas CO₂. Ms Davidson says the "Vision C" plans to be launched in two years.

The world has been extremely impressed by China's high-speed trains that cross the country by the hundreds in all directions every day, but in one corner of this vast land is a gentle reminder that life was not always this fast.

Those fortunate enough to travel to Jiayang in Sichuan province will find railway carriages dragged by steam locomotives(火车头), among the last steam trains operating in China and still running every day. First used to transport coal from Jiayang Coal Mine 62 years ago, today they transport local farmers and their produce to market and serve as a tourist attraction.

"In the early days of the railway, farmers headed for the farm produce market sitting beside coal," said Liu Chengxi, the Jiayang official in charge of the trains. "As coal production has stopped, the trains are now exclusively(专门地)for farmers and tourists."

The narrow railway, only 76.2 cm instead of the standard 144 cm, stretches for 19. 84 km, with the trains reaching a top speed of 20 km/h.

A one-way ticket costs 5 yuan for seated passengers and 3 yuan for standing passengers on the ordinary trains regardless of whether they are travelling empty-handed or with animals or vegetables. But Li Cuirong, who has worked as a train dispatcher(调度员)for more than 20 years, recommends tourists pay 80 yuan for a sightseeing train, as the carriages, which have 37 seats, are more comfortable and air-conditioned. A one-way trip takes about one and a half hours.

The scenery is dramatic as the train winds through the mountain, passengers can view chickens and geese wandering among the orange trees and butterflies dancing over the fields and ponds.

Rob Dickinson, a steam train lover from the United Kingdom, has ridden the trains twice. He hopes the narrow line can last long enough for him to find the time to get back again.

增加：在缺词处加一个漏字符号(∧)，并在其下面写出该加的词。

删除：把多余的词用斜线(\)划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1. 每处错误及其修改均仅限一词;

2. 只允许修改10处，多者(从第11处起)不计分。

To enrich students' school life, an excited competition was held on last Saturday on the school playground. Ten boys and ten girls selected by each class lined beside the rope and grasped it, eager waiting for the start. With the whistle blowing, the participants tried their best to pull the rope, while those standing by cheered desperately for him. Eventually, every students of the class won the competition was awarded a delicate notebook.

The competition was highly thought by students. Not only did it build up their bodies, but also strengthen their teamwork. Plus, the competition received positive response from parents and teachers, what made a hit in the circle of WeChat.