Questions 16 to 20 are based on the following passage.
　　The human brain contains 10 thousand million cells and each of these may have a
　　thousand connections. Such enormous numbers used to discourage us and cause us to dismiss the possibility of making a machine with humanlike ability, but now that we have grown used to moving forward at such a pace we can be less sure. Quite soon, in only 10 or 20 years perhaps, we will be able to assemble a machine as complex as the human brain, and if we can we will. It may then take us a long time to render it intelligent by loading in the right software (软件) or by altering the architecture but that too will happen.
　　I think it certain that in decades, not centuries, machines of silicon (硅) will
　　arise first to rival and then exceed their human ancestors. Once they exceed us they will be capable of their own design. In a real sense they will be able to reproduce themselves. Silicon will have ended carbon's long control. And we will no longer be able to claim ourselves to be the finest intelligence in the known universe.
　　As the intelligence of robots increases to match that of humans and as their cost declines through economies of scale we may use them to expand our frontiers, first on earth through their ability to withstand environments, harmful to ourselves. Thus, deserts may bloom and the ocean beds be mined. Further ahead, by a combination of the great wealth this new age will bring and the technology it will provide, the construction of a vast, man-created world in space, home to thousands or millions of people, will be within our power.
　　16. In what way can we make a machine intelligent?
　　A) By making it work in such environments as deserts, oceans or space.
　　B) By working hard for 10 or 20 years.
　　C) By either properly programming it or changing its structure.
　　D )By reproducing it.

　　17. What does the writer think about machines with human-like ability?
　　A) He believes they will be useful to human beings.
　　B) He believes that they will control us in the future.
　　C) He is not quite sure in what way they may influence us.
　　D) He doesn't consider the construction of such machines possible.

　　18. The word carbon( Line 4, para. 2) stands for" _______"
　　A) intelligent robots
　　B) a chemical element
　　C) an organic substance
　　D) human beings

　　19. A robot can be used to expand our frontiers when _______.
　　A) its intelligence and cost are beyond question
　　B) it is able to bear the rough environment
　　C) it is made as complex as the human brain
　　D) its architecture is different from that of the present ones

　　20. It can be inferred from the passage that _______.
　　A) after the installation of a great number of cells and connections, robots will
　　be capable of self?reproduction.
　　B) with the rapid development of technology, people have come to realize the pos
　　sibility of making a machine with human-like ability.
　　C) once we make a machine as complex as the human brain, it will possess
　　intelligence
　　D) robots will have control of the vast, man-made world in space.