跟踪导练（三）

閱读理解

A

It is a great， big， wide-open sky over our heads， but when you are flying in a jet airliner at 600 miles an hour， the sky is not so big. Thats part of the reason why， in the first four months of this year， the government said only 72 percent of all flights arrived on time， the lowest number since the recent system of reporting began in 1995.

The runways are full， the planes are jammed， and air traffic controllers complain theyre stressed out. And the radar systems that keep things going are， in large part， technology of the 1960s. “Its like driving down the road with a paper bag over your head， and youre trying to stay out of the way of other cars，” says Captain Karen Lee， a 747 pilot who heads operations for UPS， the delivery service.

At its center in Louisville， UPS is experimenting with the next generation in air traffic control： planes guided by the satellites of the Global Positioning System， instead of radar.

Though it has advanced greatly over the years， radar is a technology that dates back to World War II. It scans the sky， looking for signals from planes in the air. Typically， air traffic radar only updates a planes position once every 12 seconds or so—and in 12 seconds， a jet can move two miles or make a turn. Whats more， radar signals can be blocked by storms or mountains. But with GPS signals， pilots can see in real time exactly where they are， and where other planes are， too. A readout screen in the cockpit （驾驶舱） tells the pilots whats around them.

“What we end up with is a very exact location for each aircraft in the system，” said Basil Barimo of the Air Transport Association， which represents airlines.

1. Whats the main cause of the jamming of planes？

A. Planes fly very fast.

B. The control system has fallen behind.

C. The number of planes is increasing too fast.

D. The weather has become worse these years.

2. What will be used to solve the jamming of planes？

A. A readout screen in the cockpit.

B. A more advanced radar system.

C. A Global Positioning System.

D. A new satellite.

3. What is the disadvantage of the present radar system according to the text？

A. It sometimes loses objects.

B. It often provides unclear pictures.

C. It cannot help pilots know where they are.

D. Its signals may be limited for certain reasons.

4. It can be inferred that what matters most in the air is for the pilots .

A. to see the planes around

B. to communicate with the ground

C. to control the speed of the planes

D. to know exactly the position of each other

B

How can a creature weighing over 5 tons and normally taking 150 kilograms of food and 120 liters of water per day survive in a desert environment？

In the southwest African country of Namibia， and the Sahara lands of Mali further north， the desert elephant does just that.

Although not regarded as a separate species from the African elephant， the desert cousin differs in many ways. Their bodies are smaller， to absorb less heat， and their feet are larger for easier walking across sandy surfaces. They are taller， to reach higher branches. They have shorter tusks （象牙）， and most importantly， longer trunks to dig for water in riverbeds.

Desert elephants can travel over 70 kilometers in search for feeding grounds and waterholes， and have a larger group of families. They drink only every 3～4 days， and can store water in a “bag” at the back of their throat， which is only used when badly needed. Desert elephants are careful feeders—they seldom root up trees and break fewer branches， and thus maintain what little food sources are available. Young elephants may even eat the dung （糞便） of the female leader of a group when facing food shortage.

During drought they are unlikely to give birth to their young but with good rains the birth rate will increase greatly. Desert elephants have sand baths， sometimes adding their own urine （尿液） to make them muddy！

As we continue to overheat our weak planet， it can only be hoped that other animal species will adapt as extraordinarily well to change as the desert elephant.

5. The underlined part in Paragraph 2 means “_________”.

A. remains in the African countries

B. drinks 120 liters of water a day

C. manages to live in desert areas

D. eats 150 kilograms of food daily

6. Why are desert elephants called careful feeders？

A. They rarely ruin trees.

B. They drink only every 3～4 days.

C. They search for food in large groups.

D. They protect food sources for their young.

7. The author answers the question raised in Paragraph 1 with ________ .

A. stories and explanation B. facts and descriptions

C. examples and conclusion D. evidence and argument

8. What can be inferred from the last paragraph of the passage？

A. Overheating the earth can be stopped.

B. Not all animal species are so adaptable.

C. The planet will become hotter and hotter.

D. Not all animals are as smart as desert elephants.