37.What is said about the development of the helicopter?
A) Helicopter 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
38.Under what conditions are helicopters found to be almost indispensable?
A)For overseas passenger transportation.
B)For extremely high attitude flight.
C) For high speed transportation.
D)For urgent missions to inaccessible places.
39.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.
40.On what principle do helicopters work?
A)A combination of propellers in front and on top.
B)A propeller on top.
C)One propeller in the center of the aircraft and others at each end.
D) A propeller underneath for lifting power.
Passage Three：Questions 41 to 45 are based on the following passage.
Some individuals and citizens' groups have expressed concern about the level of violence in television programs, particularly in action-adventure series and cartoons. They argue that viewers, especially children, may learn to see violence as the only way to resolve conflicts.
Early experimental researchers compared the play of children who had seen aggressive behavior on television with the play of a control group of children who had watched nonviolent programs. Concern was intensified by findings that indicated a higher level of aggressive play in the violent-television group. Other researchers attempted to determine whether violent programs simply stimulated higher energy levels in children or actually caused them to learn violent and antisocial behavior. The results of different studies conflicted. Some researchers claimed that televised violence actually had a positive cathartic effect, allowing some viewers to release heightening tensions; these findings however, were not confirmed in further studies. Other scholars pointed out that both prosocial and. antisocial behavior can be learned from television.
Social scientists find .it especially difficult to assess accurately the subtle, cumulative (累积的) effects of vie-wing a broad variety of television programs throughout childhood. Distinguishing the possible effects of television from other influences at home and at school is also difficult. Current research suggests that moderately higher levels of antisocial behavior can be traced to television viewing, but further study needs to be done to confirm it.
Because of the long-standing tradition in the U.S. of freedom of speech and of the press, the government would probably not attempt to directly limit or censor the appearance of violence on television. Among the networks and producers, pressure from concerned citizens continues to be balanced by the increasing popularity of high-energy action-adventure programs.
41. What is the passage mainly about?
A. Violence in television programs.
B. Levels of violence in action adventure series and cartoons.
C. Educational programs for children.
D. Researches on television programs..