单选题：根据下面资料，回答题 How do the Movies Do It? ① Have you ever seen a m

根据下面资料，回答题
How do the Movies Do It?
① Have you ever seen a movie in which a building was burned down or a bridge was destroyed? Have you seen films in which a train crashed or a ship sank into the ocean? If so,you may have wondered how these things could happen without harming the people in the film.
② The man who knows the answer is the "special-effects" man. He has one of the most important jobs in the film industry. He may be ordered to create a flood or to make a battlefield explode. But he may also be asked to create a special effect which is much less exciting, though just as important to the success of the film.
③In a scene for one movie, there was a big glass bowl filled with water in which small fish were swimming. The director of the movie wanted the fish to stop swimming suddenly while they seemed to stare at an actor. Then the director wanted the fish to stop staring and swim away. But fish cannot be ordered to do anything. It was quite a problem. The special-effects man thought about this problem for a long time. The result was an idea for controlling the fish with a harmless use of electricity. First, he applied electricity to the fish bowl, causing the fish to be absolutely still. Then he rapidly reduced the amount of electricity, allowing the fish to swim away. Thus, he got the humorous effect that the director wanted.
④ As in other parts of movie making, there are those who have developed particular skills in creating certain kinds of effects. For fires, the special-effects man does not trust the normal burning process of wood or other materials. He does not have time to wait until large flames appear. Usually he places metal pipes in the area that is to be burned. Gas flowing through the pipes burns instantly but can be kept under control easily by opening or closing the pipes.
⑤All this requires training, skill, and experience. It also adds a great deal to the expense of producing the film. It helps explain why so many movies are very expensive to make.

How could these disasters happen without in the film?