单选题
Flight simulator refers to any electronic or mechanical system for training airplane and spacecraft pilots by simulating flight conditions. The purpose of simulation is not to completely substitute【C1】______actual flight training but to thoroughly familiarize students with the vehicle【C2】______before they undergo extensive and possibly dangerous actual flight training. 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【C3】______simple aircraft maneuvers in three dimensions: nose up or down; left wing high and right low, or vice versa; and yawing to left or right. Until 1929, however, a truly effective simulator, the Link Trainer devised by Edwin A. Link, a self-educated aviator and inventor, appeared.【C4】______, airplane instrumentation had been developed sufficiently to permit " blind" flying on instruments alone, but training pilots to do so involved【C5】______risk. Link built a model of an airplane cockpit equipped【C6】______instrument panel and controls that could simulate all the movements of an airplane. Pilots could use the device for instrument training, manipulating the controls【C7】______instrument readings so as to maintain straight and level flight or controlled climb or descent with no visual reference【C8】______any horizon except for the artificial one on the instrument panel. The trainer was modified【C9】______aircraft technology advanced. Commercial airlines began to use the Link Trainer for pilot training, and the U. S. government began purchasing them in 1934,【C10】______thousands more as World War II approached.