题目内容：

Dec 21st 2018

On December 19th Gatwick airport, Britain’s second-biggest, was forced to close due to several sightings of drones（无人机）flying near its runways. The airport only reopened on the morning of December 21st.   ①  .

The potential for an incident of this scale has been recognized for some years now. The falling price of small drones in recent years has resulted in the number flying dangerously near aircraft to rise sharply.   ②  .

This is a threat that the authorities have to take seriously. Recent research suggests that small unmanned aerial vehicles (UAVs) can be much more damaging than birds — a surprisingly common cause of aircraft crashes — at the same impact speed, even if they are a similar weight. The researchers found that the drones’ rigid and dense materials—such as metal, plastic and lithium batteries—can put aero planes at much greater risk than a bird carcass（动物尸体）. If a drone were to hit an aircraft’s fan blades when it is operating at its highest speed, the blades could break and power to the engine could be lost.

③  . But it also underlined the potential for destruction that drones afford. The British police do not think that terrorism was the motivation behind the latest incident at Gatwick. According to the Daily Telegraph, a British newspaper, environmental activists are suspected of being behind the attack, which has happened before.

As attention turns to what can be done to prevent a repeat, two solutions stand out. The first is regulation. Regulators in America and Britain already ban drones from flying too close to airports. America has introduced a compulsory registration scheme for drones and Britain plans to follow suit.

But as the chaos at Gatwick shows, even serious punishments will not stop those intending to cause harm deliberately.   ④  . Technology is the second, and more important, answer to the threat. In the US the FAA has experimented with a system. Drones can have pre-programmed software that keeps them away from prohibited areas, an approach known as “geofencing”. British engineers have come up with a system that catches drones with a net and then softly lands them with a parachute. Dutch police have even attempted to train eagles to catch drones in the sky and return them to their trainers as if they were song birds. The closure at Gatwick will give ideas such as these a mighty push forward.

1.Compared to birds, drones have become a more serious threat to airplane crash in that _____.

A.drones are much heavier than birds in general

B.drones usually fly even faster than birds

C.drones will attack airplanes on purpose

D.drones are made of rigid and dense materials

2.The sentence “The extended closure of Gatwick was a justified response to this threat.” should be put in _____.

A.① B.②

C.③ D.④

3.It can be inferred from the article that _____.

A.The decreasing size of drones recently has led to frequent accidents of this kind.

B.Among the solutions, technology is considered to be a more reliable one.

C.The FAA has adopted a “geofencing” system with the help of trained eagles.

D.The British police think environmentalists conducted the latest incident at Gatwick.

4.What can be a suitable title for the article?

A.Drones or birds, which is more harmful?

B.How to stop unmanned aerial vehicles?

C.Several drones close Gatwick airport.

D.Drones have become a pressing issue.