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  3. While chemists try to assemble molecules using a combination of theoretical principles and practical experience to mold m

While chemists try to assemble molecules using a combination of theoretical principles and practical experience to mold m

admin2011-01-17  58
问题            While chemists try to assemble molecules using a combination of theoretical
       principles and practical experience to mold molecules that have desired
       structural and chemical properties, nanotechonologists generally seek to make
Line    more than a single molecule. They build arrays of identical or complexed
(5)      molecules, sometimes on a scale that will transcend the boundaries of the
       microscopic and approach the macroscopic, using both top-down and bottom-up
       approaches. The first is exemplified by scientists who build objects and
       molecular arrays using the techniques of scanning probe microscopy, while the
       second is exemplified by investigators who design two-and three-dimensional
(10)     chemical systems that cohere according to the rules of chemical interactions.
       The top-down approach has exquisite precision, but its disadvantage is its lack
       of extensive parallelism; it requires manipulating atoms and molecules
       practically one by one, while the bottom-up approach is massively parallel. But
       in both cases, scientists are forced to use the difficult nanometer scale, i.e. the
(15)     level at which living systems tend to make their structural components, rather
       than the angstrom scale of chemistry.
It can be inferred from the passage that the author believes which of the following concerning the top-down method of nanotechnology?
选项 A、The top-down method tends to be accurate but highly inefficient, resulting in a process that takes a great deal of time and energy.
B、The top-down method, unlike the bottom-up method, tends to disobey the rules of many chemical interactions.
C、The top-down method requires a greater level of technological involvement than does the bottom-up method.
D、The top-down method shows the limits of nanotechnology methods that rely too heavily on parallel processes.
E、The top-down method is fairly useless when applied to the problem of creating a single molecule.
答案A
解析
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