Compared with the robot, the human worker is undoubtedly superior. He is capable of performing a wider variety of work. Moreover, he is able to adapt his working pattern in order to cope with changing situations which the robot cannot do. On the other hand, the human worker is relatively weak and cannot tolerate work in extreme conditions such as extremely high or low temperatures. Consequently, we find humans and robots working together in many areas of work. Robots are used to perform. dangerous tasks so that their human operators need not risk their lives. To handle harmful radioactive materials, such as uranium (铀), robots in the form. of machined arms are used so the human operators can stay from the fatal rays. Another advantage of the robot is that it never complains about long working hours or that it is boring. It works around the clock and performs equally well in any situation. It needs little servicing and absolutely no holidays. That is why many of them are used to replace human workers for simple and repetitive jobs. The car manufacturers, for example, were amongst the first to use robots to replace workers working on the assembly line. They take over such boring tasks as tightening nuts and screws and spraying paint. Released from these unrewarding tasks, the human worker can be trained for more fulfilling posts, where he can make full use of his ability and get satisfaction from them. The management, on the other hand, will also benefit from these 'human pretenders' as they form. a new work force which is able to produce more at a lower cost. Looking to the future, we can expect tomorrow's robots to be even more 'intelligent' than those of today. Humans and robots worked together in many areas of work because ______.