Hollywood’s true heroes are losing their jobs. Stunt people (替身演员) who entertained cinema-goers by failing for the sky, swimming with sharks and driving fast cars have been replaced by technology. After generations of street fights, high falls, and setting fire to themselves, these people have had nearly all their work replaced by computers. The most dangerous and costly stunts can now be achieved by mixing computer picture with live action.In the mid-1990s there were 12,000 registered stunt people, but more than half of them had difficulty finding work. Sometimes, six or seven teams would be working on a film. Then, after a few days, the producers would come in and say, "You can go home."The reason was simple: cost. Computer technology made it possible to create stunts which would either be too expensive or too dangerous to attempt. With the rise of digital technology (数字技术), insurance companies became more reluctant to cover real stunts. "If they know it can be clone safely with visual effects, the companies will not insure real stunts," said a stunt person.Many in their industry believe stunt people should develop expertise in the new technology, acting as advisers on the virtual stunts. Some, however, think that stunt people can survive in their traditional careers. They believe that audiences won’t accept stunts produced by computers for too long. The purpose of this passage is to（）

A. promote the use of real stunts in the film-making
B. describe the working scenes of the stunt people
C. recommend jobs to the stunt people
D. introduce the difficult situation of the stunt people at work