题目内容：

Today, air travel is far safer than driving a car on a busy motorway. But still there is a danger that grows every year. Airliners get larger and larger. Some airplanes can carry over 300 passengers. And the air itself becomes more and more crowded. If one large airliner struck into another in midair, 600 lives could be lost.

From the moment an airliner takes off to the moment it lands, every movement is watched on radar screens. Air traffic controllers tell the pilot exactly when to turn, when to climb and when to come down.

The air traffic controllers around a busy airport like London, Heathrow may deal with 2,500 planes a day. Not all of them actually land at the airport. Any plane that flies near the airport comes under the orders of the controllers there. Even a small mistake on their part could cause a terrible accident.

Recently such a disaster almost happened. Two large jets were flying towards the airport. One was carrying 69 passengers from Toronto, the other 176 passengers from Chicago. An air traffic controller noticed on his radar（雷达） screen that the two planes were too close to each other. He ordered one to turn to the right and to climb. But he made a mistake. He ordered the wrong plane to do this. So, instead of turning away from the second plane the first plane turned towards it. Fifteen seconds later, it flew directly in front of the second plane. They avoided each other by the smallest part of a second. The distance between them was less than that of a large swimming pool. This is an example of the danger that grows every year.

1.The air traffic controllers of an airport _______.

A. control all the planes flying near the airport

B. give orders to planes leaving the airport

C. only deal with the planes that want to land there

D. are allowed to handle 250 planes a day

2.The danger of air crashes（碰撞） grows every year because ________.

A. airliners are getting larger and air traffic is becoming heavier

B. a pilot does not always hear a controller’s order

C. a controller is likely to make more and more mistakes

D. airports can hardly serve the growing number of airplanes

3. The example in the passage is to show that _______.

A. air traffic controllers are often careless

B. air traffic controllers should pay much attention to avoiding accidents

C. it is difficult for airplanes to avoid terrible accidents

D. two planes should not fly too close to each other