D. Its favourable climate.

25. What do we now about those who first dug for gold in Dawson? A. Two-thirds of them stayed there. B. One out of five people got rich. C. Almost everyone gave up. D. Half of them died.

26. What was the main reason for many people to leave Dawson? A. They found the city too crowded. B. They wanted to try their luc elsewhere. C. They were unable to stand the winter. D. They were short of food. 27. What is the tet mainly about? A. The rise and fall of a city. B. The gold rush in Canada. C. Journeys into the wilderness. D. Tourism in Dawson.

【话题解读】这是一篇说明文。文章主要介绍了Dawson这座城市的发展原因、过程与现状。 24.C

【解析】细节理解题。根据文章第一段中Cities usually have a good reason for being where they are, lie a nearby port or river. People settle in these places because they are easy to get to and naturally suited to communications and trade. New Yor City, for eample, is near a large harbour at the mouth of the Hudson River.可知，人们选择在河边或港口设城是因为交通方便，便于做生意。而纽约就是在哈德森河口附近的一个大港口，故纽约吸引早期移民的原因是它的地理位置，故C正确。 25.B

【解析】细节理解题。根据文章第二段最后一句Of the first 20,000 people who dug for gold, 4,000 got rich. About 100 of these stayed rich men for the rest of their lives.可知，在最初挖黄金的两万人中有4000人变富有，所以是五分之一的人变富了，故B正确。 26.B

【解析】细节理解题。根据文章最后一段中and when they heard there were new gold discoveries in Alasa, they left Dawson City as quicly as they had come.可知，人们离开Dawson的主要原因是听说在Alasa发现了黄金，

也就是他们要去别的地方寻找发财的机会。故B正确。 27.A

【解析】主旨大意题。第一段简要介绍城市发展的原因，引出Dawson这一城市的兴起，第二段介绍了该城市兴起的原因，第三段介绍人们选择离开该城市的原因及现在的状况，所以全文围绕Dawson这个城市的发展起伏。故A正确。

4.【2018·北京卷，C】

Plastic-Eating Worms

Humans produce more than 300 million tons of plastic every year. Almost half of that winds up in landfills(垃圾填埋场), and up to 12 million tons pollute the oceans. So far there is no effective way to get rid of it, but a new study suggests an answer may lie in the stomachs of some hungry worms.

Researchers in Spain and England recently found that the worms of the greater wa moth can brea down polyethylene, which accounts for 40% of plastics. The team left 100 wa worms on a commercial polyethylene shopping bag for 12 hours, and the worms consumed and broe down about 92 milligrams, or almost 3% of it. To confirm that the worms’ chewing alone was not responsible for the polyethylene breadown, the researchers made some worms into paste(糊状物) and applied it to plastic films. 14 hours later the films had lost 13% of their mass — apparently broen down by enymes (酶) from the worms’ stomachs. Their findings were published in Current Biology in 2017.

Federica Bertocchini, co-author of the study, says the worms’ ability to brea down their everyday food — beeswa — also allows them to brea down plastic. ＂Wa is a comple miture, but the basic bond in polyethylene, the carbon-carbon bond, is there as well, ＂she eplains, ＂The wa worm evolved a method or system to brea this bond. ＂

Jennifer DeBruyn, a microbiologist at the University of Tennessee, who was not involved in the study, says it

is not surprising that such worms can brea down polyethylene. But compared with previous studies, she finds the speed of breaing down in this one eciting. The net step, DeBruyn says, will be to identify the cause of the breadown. Is it an enyme produced by the worm itself or by its gut microbes(肠道微生物)?

Bertocchini agrees and hopes her team’s findings might one day help employ the enyme to brea down plastics in landfills. But she epects using the chemical in some ind of industrial process — not simply ＂millions of worms thrown on top of the plastic. ＂

43. What can we learn about the worms in the study? A. They tae plastics as their everyday food. B. They are newly evolved creatures. C. They can consume plastics. D. They wind up in landfills.

44. According to Jennifer DeBruyn, the net step of the study is to . A. identify other means of the breadown B. find out the source of the enyme C. confirm the research findings D. increase the breadown speed

45. It can be inferred from the last paragraph that the chemical might . A. help to raise worms B. help mae plastic bags C. be used to clean the oceans D. be produced in factories in future 46. What is the main purpose of the passage? A. To eplain a study method on worms. B. To introduce the diet of a special worm. C. To present a way to brea down plastics. D. To propose new means to eep eco-balance.

【文章大意】本文为说明文。文章介绍了一种吃塑料的虫子大蜡螟，它胃中的酶能够降解塑料，这为解决塑料污染提供了新的途径。

43.C 【解析】细节理解题。根据文章第三段Federica Bertocchini, co-author of the study, says the worms’ ability

to brea down their everyday food — beeswa — also allows them to brea down plastic. 可知，研究结果发

现，蠕虫分解日常食物的能力让它们可以分解塑料，也就是说它们可以消费塑料。故选C。 44.B 【解析】细节理解题。根据文章第四段The net step, DeBruyn says, will be to identify the cause of the

breadown. Is it an enyme produced by the worm itself or by its gut microbes(肠道微生物)?可知，下一步研 究是辨清分解的原因，查明这种酶于哪里，是虫子自己产生的还是它肠道里的微生物产生的。故选B。45.D 【解析】推理判断题。根据文章最后一段But she epects using the chemical in some ind of industrial process

— not simply ＂millions of worms thrown on top of the plastic. ＂可以推断出，Bertocchini希望这种化学物质将能在工业生产中使用，而不是仅仅依靠蠕虫分解塑料。故选D。

46.C 【解析】写作意图题。根据文章第一段最后一句So far there is no effective way to get rid of it, but a new

study suggests an answer may lie in the stomachs of some hungry worms. 可知，有一种新的方法被用于分解塑料。再根据最后一段最后一句But she epects using the chemical in some ind of industrial process — not simply ＂millions of worms thrown on top of the plastic. ＂可知，Bertocchini希望将这种方法推广到工业中。由此可以推知写作意图为介绍一种分解塑料的方法。故选C。 5.【2018·天津卷，C】

There’s a new frontier in 3D printing that’s beginning to come into focus food. Recent development has made possible machines that print, coo, and serve foods on a mass scale. And the industry isn’t stopping there. Food production

With a 3D printer, a coo can print complicated chocolate sculptures and beautiful pieces for decoration on a wedding cae. Not everybody can do that — it taes years of eperience, but a printer maes it easy. A restaurant in Spain uses a Foodini to “re-create forms and pieces” of food that are “eactly the same,” freeing coos to complete other tass. In another restaurant, all of the dishes and desserts it serves are 3D-printed, rather than farm to table. Sustainability(可持续性)

The global population is epected to grow to 9.6 billion by 2050, and some analysts estimate that food production will need to be raised by 50 percent to maintain current levels. Sustainability is becoming a necessity. 3D food printing could probably contribute to the solution. Some eperts believe printers could use hydrocolloids (水解胶体) from plentiful renewables lie algae(藻类) and grass to replace the familiar ingredients(烹饪原料). 3D printing can reduce fuel use and emissions. Grocery stores of the future might stoc \freeing up shelf space and reducing transportation and storage requirements. Nutrition

Future 3D food printers could mae processed food healthier. Hod Lipson, a professor at Columbia University, said, “Food printing could allow consumers to print food with customied nutritional content, lie vitamins. So