For centuries man had dreamed of achieving vertical flight. 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 “Helix”, which could carry a man straight up but this was only a design and never tested.
The ancient dream was finally realized in 1940 when a Russian immigrant, an aeronautical engineer, piloted a strange-looking craft of steel tube 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 personal helicopter. Every man would have one in his backyard. People anticipated that vertical flight transports would carry millions of passengers as the airlines of today do. 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 to places where other aircrafts 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 likely a 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.

11. What is a helicopter?
A. An aircraft that can go faster than the ordinary airplane.
B. An aircraft that fits into the smallest possible place.
C. An aircraft that can fly up vertically
D. An aircraft that is used only for commercial service.
12. 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 airplane.
D. Some people thought they would become widely used by the average individual.
13. Under what condition are helicopters found to be almost indispensable?
A. For overseas passenger transportation
B. For extremely high altitude
C. For high speed transportation
D. For urgent missions to inaccessible places
14. 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 high-flying jets.
C. They are often used for rescue work.
D. They are now used exclusively for commercial projects
15. What principle do helicopters work on?

11 什么是直升机？
The ancient dream was finally realized in 1940 when a Russian immigrant, an aeronautical engineer, piloted a strange-looking craft of steel tube 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.
所以选C
12 直升机的发展
A肯定错，C文章没有提到他的危险性比其他的大 D的话文章也没说他的广泛性能应用于每个人，我任务是B
13是D为紧急任务无法进入的地方，在文章最后一段
14是C，也是最后一段
15它的工作原理
The ancient dream was finally realized in 1940 when a Russian immigrant, an aeronautical engineer, piloted a strange-looking craft of steel tube 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.

参考文献：个人分析，尽供参考