You are watching a film in which two men are having a fight. They hit one another hard. At the start they only fight with their fists .But soon they begin hitting one another over the heads with chairs. And so it goes on until one of the men crashes through a window and falls thirty feet to the ground below. He is dead! Of course he isn't really dead. With any luck he isn't even hurt. Why ? Because the men who fall out of high windows or jump from fast moving trains, who crash cars of even catching fire, are professionals .They do this for a living. These men are called stuntmen. That is to say, they perform tricks . There are two sides to their work. They actually do most of the things you see on the screen. For example, they fall from a high building. However, they do not fall on to hard ground but on to empty cardboard boxes covered with a mattress . Again, when they hit one another with chairs, the chairs are made of soft wood and when they crash through windows, the glass is made of sugar! But although their work depend on trick of this sort, it also requires a high degree of skill and training. Often a stuntman's success depends on careful timing .For example, when he is "blown up" in a battle scene, he has to jump out of the way of the explosion just at the right moment. Naturally stuntmen are well paid for their work, but they lead dangerous lives. They often get seriously injured, and sometimes killed. A Norwegian stuntman, for example, skied over the edge of a cliff a thousand feet high. His parachute failed to open, and he was killed. In spite of all the risks, this is no longer a profession for men only. Men no longer dress up as women when actresses have to perform some dangerous action. For nowadays there are stuntgirls too! Which of the following is the main factor  of a successful performance?
Strength Exactness Speed Carefulness