The author compares the hypothetical literature on air-traffic control with _____________.

Directions: Read the following passage & answer the question. 
           
            During World War II, an inventor submitted a scheme for building a giant airship armed with death rays to the British government. He had provided details of the engines, navigational system, etc. when question about the death-ray themselves he exclaimed, “Oh, I thought the military had plenty of them available,”
            If a robot is defined, provisionally, as a machine made in the image of man, then it must be stated that like death – rays in 1940, robots in 1990 remain in the world of speculation not of established fact yet, just as the inventor took the existence of death – rays for granted and concentrated on putting them to use the popular imagination has been much more preoccupied by the question of what we should do when robots do arrive than with the business of actually making them , it is rather as if the Wright brothers first flight had been preceded by an extensive literature on air – traffic control .

            The prevailing image on the robots as a walking talking mechanical man is firmly established in our consciousness. It is worth pondering how this nation–a hypothesis, took on so vivid a form. There are, it is true, machines in existence which we have, perhaps rather prematurely, categorized as robots. But long before even this primitive vanguard became a practical proposition the idea of the robots was enjoying a lively existence in human imagination. It seem to have been around even before it gained a name. Other inventions had to take concrete.