单选题 For centuries man dreamed of achieving vertical height. In 400 A. D. Chinese children played with a fan-like toy that spun upwards and fell back to earth as rotation ceased. Leonardo da Vinci conceived the first mechanical apparatus, called a "Helix", which could carry a man straight up, but this was only a design and was never tested.
The ancient dream was finally realized in 1940 when a Russian immigrant, an aeronautical engineer, piloted a strange-looking craft of steel tubing with a rotating fan on top. It rose awkwardly and vertically into the air from a standing start, hovered a few feet above the ground, went sideways and backwards, and then settled back to earth. That vehicle was called a helicopter.
Imaginations were fired. Men dreamed of commuting to work in their own personal helicopter. Every man would have one in his backyard. People anticipated that vertical flight transports would carry millions of passengers as do the airliners of today. Such fantastic expectations were not fulfilled.
The helicopter has now become an extremely versatile machine. It excels in military missions, carrying troops, guns and strategic instruments where other aircraft cannot go. Corporations use them as airborne offices, many metropolitan areas use them in police work, construction and logging companies employ them in various advantageous ways, engineers use them for site selection and surveying, and oil companies use them as the best way to make offshore and remote work stations accessible to crews and supplies. Any urgent mission to a hard-to-get-to place is a likely task for a helicopter. Among their other multitude of uses, they deliver people across town, fly to and from airports, assist in rescue work, and aid in the search for missing or wanted persons.

单选题 A helicopter is an aircraft that

A. can go faster than the ordinary airplane
B. can fit into the smallest possible place
C. can fly vertically into the air
D. is used only for commercial service

【正确答案】 C

【答案解析】文章第二段二、三句对helicopter作了详细描述，据此可知答案C为正确答案。

单选题 What is said about the development of the helicopter?

A. Helicopters have only been worked on by man since 1940.
B. An Englishman was the first to achieve flight in a helicopter.
C. Helicopters were considered more dangerous than the early airplanes.
D. Some people thought they would become widely used by the average individual.

【正确答案】 D

【答案解析】A项中的only过于绝对，不可选；B项中的Englishman与文中的Russian immigrant相悖；C项文中未提及；而文章最后一段详述了helicopter的种种用途，符合题意，故为正确答案。

单选题 Under what conditions are helicopters found to be almost indispensable?

A. For overseas passenger transportation.
B. For extremely high altitude flight.
C. For high-speed transportation.
D. For urgent missions to inaccessible places.

【正确答案】 D

【答案解析】直升机无论在速度还是高度上都是有限的，故B、C不可选；而文章最后一段第二句句意与D项符合，故为正确答案。

单选题 How has the use of helicopters developed?

A. Each year they have become larger to accommodate greater loads.
B. They are taking the place of highflying jets.
C. They are often used for rescue work.
D. They are now used exclusively for commercial projects.

【正确答案】 C

【答案解析】A、B两项在文中并未得到体现，故可排除；D项中的exclusively过于绝对，亦不可选；而C项在文章的最后一句中得以体现，故为正确答案。

单选题 On what principle do helicopters work?

A. A combination of propellers in front and on top.
B. A rotating propeller topside.
C. One propeller in the center of the aircraft and others at each end.
D. A propeller underneath for lifting power.

【正确答案】 B

【答案解析】依据文章第二段第一句The ancient dream was finally realized in 1940 when a Russian immigrant，an aeronautical engineer，piloted a strange-looking craft of steel tubing with a rotating fan on top可知，答案为B。