Stage 5.

A human being is a soft, weak creature. It needs constant supplies of air, water, and food; it has to spend a third of its life asleep, and it can't work if the temperature is too hot or too cold. But a robot is made of strong metal. It uses electrical energy directly, never sleeps, and can work in any temperature. It is stronger, more efficient - and sometimes more human than human beings. Isaac Asimov was one of the greatest science-fiction writers, and these short stories give us an unforgettable and terrifying vision of the future.