Flight simulator （飞行模拟器） refers to any electronic or mechanical system for training airplane and spacecraft pilots and crew member by simulating flight conditions. The purpose of simulation is not to completely substitute （1） actual flight training but to thoroughly familiarize students with the vehicle （2） before they （3） extensive and possibly dangerous actual flight training. Simulations also is useful for review and for familiarizing pilots with new （4） to existing craft.
　　Two early flight simulators appeared in England within a decade after the first flight of Orville and Wilbur Wright. They were designed to enable pilots to simulate simple aircraft （5） in three dimensions， nose up or down； left wing high and right low， or vice versa； and （6） to left or right. It took until 1929， however， for a truly effective simulator， the Link Trainer， to appear， devised by Edwin A. Link， a self-educated aviator and inventor from Binghamton， New York. （7） airplane instrumentation had been developed sufficiently to permit "blind" flying on instruments alone， but training pilots to do so involved （8） risk. Link built a model of an airplane cockpit equipped （9） instrument panel and controls that could realistically simulate all the movements of an airplane. Pilots could use the device for instrument training， manipulating the controls （10） instrument readings so as to maintain straight and level flight or （11） climb or descent with no visual reference （12） any horizon except for the artificial one on the instrument panel. The trainer was modified （13） aircraft technology advanced. Commercial airlines began to use the Link Trainer for pilot training， and the US government began purchasing them in 1934， （14） thousands more as World War II approached.
　　Technological advances during the war， particularly in electronics， helped to make the flight simulator increasingly （15） The use of efficient analog computers in the early 1950s led to further improvements. Airplane cockpits， controls， and instrument displays had by then become so inpidualized that it was no longer feasible to use a generalized trainer to prepare pilots to fly anything （16） the simplest light planes. By the 1950s， the US Air Force was using simulators that precisely （17） the cockpits of its planes. During the early 1960s （18） digital and hybrid computers were adopted， and their speed and flexibility revolutionized simulation systems. Further advances in computer and （19） technology， notably the development of virtual-reality simulation， have made it possible to （20） highly complex real-life conditions.
　　1. A. for B. to C. with D. on
　　2. A. concerning B. concern C. being concerned D. concerned
　　3. A. undertake B. undergo C. underplay D. underuse
　　4. A. models B. modifications C. modifiers D. modica
　　5. A. manifestations B. manipulations C. manifestoes D. maneuvers
　　6. A. yawling B. yawning C. yawing D. yawping
　　7. A. From then on B. From now on C. By now D. By then
　　8. A. considerable B. considerate C. considering D. considered
　　9. A. for B. in C. with D. on
　　10. A. on the part of B. on the basis of C. on the track of D. on the verge of
　　11. A. control B. controllable C. controlled D. controller
　　12. A. to B. for C. on D. in
　　13. A. as for B. as to C. as D. for
　　14. A. acquiring B. requiring C. sustaining D. retaining
　　15. A. actual B. realistic C. realizing D. true
　　16. A. except B. except for C. apart from D. but
　　17. A. replenished B. replaced C. replicated D. reposed
　　18. A. electronic B. electric C. electricity D. electron
　　19. A. program B. programmable C. programmed D. programming
　　20. A. resurrect B. reproduce C. resuscitate D. resume
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