The first robot was invented in the 1920s. Robots have appeared in many American films. In some films, they are stronger, faster and cleverer than people. In real life, robots are mainly used in factories. They do some dangerous and difficult jobs for humans. Robots also help disabled people, for example, blind people. Today many blind people have a guide dog to help them. In the future, guide dogs might be robot dogs. One kind of robot guide dog has wheels. It moves in front of the owner. It is very clever. It knows the speed of its owner's walk. The owner wears a special belt. The belt sends instructions to the owner from the dog, such as "Stop here" "Turn left" or "Turn right". In the United States, another kind of robot helps disabled people to take care of themselves in their daily life. The robot hears the sound of its owner's voice. It follows instructions such as. "Turn the page" or "Make a cup of coffee". Robots are also used in American hospitals. They can do simple jobs. At one hospital, for example, a robot takes meals from the kitchen to patients' rooms. It never gets lost because this robot has a map of the hospital in its computer memory. Though robots can help people in many different ways, they will never take the place of humans. ,. From the passage, we know robots cannot be  _  .
dangerous animals factory workers guide dogs hospital helpers