第二篇 Please Fasten Your Seatbelts
Severe turbulence (湍流) can kill aircraft passengers. Now, in test flights over the Rocky Mountains, NASA (美国航空航天局) engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.
Clear-air turbulence often catches pilots by surprise. Invisible to radar, it is difficult to forecast and can hurl (用力抛出去) passengers about the cabin. In December 1997, one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 metres in a few seconds.
However, passengers can avoid serious injury by fastening their seatbelts. "It is the only antidote (对策) for this sort of things," says Rod Bogue, project manager at NASA’s Dryden Flight Research Center in Edwards, California.
The centre’s new turbulence detector is based on lidar, or laser radar, Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler effect. The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air, the speed equals the plane’s airspeed. But as the particles swirl (打漩) in rough air, their speed of approach increases or decreases rapidly. The rate of change in speed corresponds to the severity (激烈程度) of the turbulence.
In a series of tests that began last month, a research jet flew repeatedly into disturbed air over the mountain ridges (山脉) near Pueblo, Colorado. The lidar detector spotted turbulence between 3 and 8 kilometres ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.
Bogue says that he had " a comfortable amount of time" to fasten his seatbelt. The researchers are planning to improve the lidar’s range with a more powerful beam. The system could be installed on commercial aircraft in the next few years.
36. What does "clear-air turbulence" probably mean? (Paragraph 1)
A A not very rough storm.
B Unexpected disturbed air.
C A kind of visible storm.
D A storm over mountain ridges.
37. In December 1997, a United Airlines flight hit unexpected rough air,
A causing a lot of damage to the plane.
B throwing its passengers out of the cabin.
C resulting in heavy casualties.
D forcing the pilot to make an emergency landing.
38. The turbulence detector can tell the severity of the turbulence by measuring
A the speed of the plane.
B the speed of the light.
C the number of particles in the air.
D the changes of the particles’ speed.
39. We can infer from the fifth paragraph that
A the lidar detector can successfully forecast turbulence.
B researchers are not sure about the effectiveness of the lidar detector.
C passenger planes will be used in further experiments.
D no more test flights are needed.
40. The last paragraph tells us, among other things, that
A the lidar detector needs improvement.
B many airlines are interested in the system.
C passengers often forget to fasten their seatbelts.
D the lidar detector can be used in a wide range of areas.
第三篇 "Salty" Rice Plant Boosts Harvests
British scientists are breeding a new generation of rice plants that will be able to grow in soil containing salt water. Their work may enable abandoned farms to become productive once more.
Tim Flowers and Tony Yeo, from Sussex University’s School of Biological Sciences, have spent several years researching how crops, such as rice, could be made to grow in water that has become salty.
The pair have recently begun a three-year programme, funded by the Biotechnology and Biological Sciences Research Council, to establish which genes enable some plants to survive salty conditions. The aim is to breed this capability into crops, starting with rice.
It is estimated that each year more than 100 hectares (公顷) of agricultural land are lost because salt gets into the soil and stunts (妨碍生长)plants. The problem is caused by several factors. In the tropics, mangroves (红树林) that create swamps (沼泽) and traditionally formed barriers to sea water have been cut down. In the Mediterranean, a series of droughts have caused the water table to drop, allowing sea water to seep (渗透) in. in Latin America, irrigation often causes problems when water is evaporated (蒸发) by the heat, leaving salt deposits behind.
Excess salt then enters the plants and prevents them functioning normally. Heavy concentrations of minerals in the plants stop them drawing up the water they need to survive.
To overcome these problems, Flowers and Yeo decided to breed rice plants that take in very little salt and store what they do absorb in cells that do not affect the plants’ growth. They have started to breed these characteristics into a new rice crop, but it will take about eight harvests before the resulting seeds are ready to be considered for commercial use.
Once the characteristics for surviving salty soil are known, Flowers and Yeo will try to breed the appropriate genes into all manners of crops and plants. Land that has been abandoned to nature will then be able to bloom again, providing much needed food in the poorer countries of the world.
41 Which of the following statements about Flowers and Yeo is true?
A They are students at Sussex University.
B They are rice breeders.
C They are husband and wife
D They are colleagues at an institution of higher learning.
42 Flowers and Yeo have started a programme
A to find ways to prevent water pollution.
B to identify genes that promote growth in salty soil.
C to breed rice plants that taste salty.
D to find ways to remove excessive salt from soil.
43 Which of the following is NOT mentioned as a cause of the problem discussed in the passage?
A Natural barriers to sea water have been destroyed.
B The water table has gone down after droughts.
C Sea level has been continuously rising.
D Evaporation of water leaves salt behind.
44 The word "affect" in Paragraph 6 could be best replaced by
A "influence"
B "effect"
C "stop"
D "present"
45 The attitude of the author towards the research project is
A positive
B negative.
C suspicious
D indifferent.
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