28-28: Which of the following most logically completes the argument? A certain cultivated herb is one of a group of closely related plants that thrive in soil with high concentrations of metals that are toxic to most other plants. Agronomists studying the herb have discovered that it produces large amounts of histidine, an amino acid that, in test-tube solutions, renders these metals chemically inert. Possibly, therefore, the herb’s high histidine production is what allows it to grow in metal-rich soils, a hypothesis that would gain support if ______. A: histidine is found in all parts of the plant – roots, stem, leaves, and flowers B: the herb’s high level of histidine production is found to be associated with an unusually low level of production of other amino acids C: others of the closely related group of plants are also found to produce histidine in large quantities D: cultivation of the herb in soil with high concentrations of the metals will, over an extended period, make the soil suitable for plants to which the metals are toxic E: the concentration of histidine in the growing herb declines as the plant approaches maturity 16: In recent years, networks of fiber-optic cable have been replacing electrical wire for transmitting telecommunications signals. Signals running through fiber-optic cables deteriorate, and so the signals must be run through a piece of equipment called a regenerator before being transmitted father. Light-Line is the leading manufacturer of signal regenerators. Therefore, Light-line is one of the companies that will most benefit if new long-distance fiber-optic telecommunications networks are constructed. Which of the following, if true, casts the most doubt on the prediction about light-ling’s prospects? A: Telecommunications signals sent along electrical wires can travel much farther than signals transmitted through fiber-optic before needing to be regenerated. B: Expanding its production of regenerators will require Light-line to spend proportionately more on labor and materials. C: The volume of signals that a fiber-optic cable can carry is several thousand times greater than the volume that can be carried by an electrical wire of similar size. D: There are technologies that enable telecommunications signals to be transmitted without either wire or fiber-optic cable. E: Several manufacturers are developing regenerator technologies that will allow signals to be transmitted many times farther than at present before requiring regeneration. 28-28答案是哪个,why？31-16为什么是c呢?请教牛牛
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发表于 2005-11-28 22:57:00
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