According to the passage, the five well-known plant hormones are not useful in controlling the growth of crops because______ Th

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问题 According to the passage, the five well-known plant hormones are not useful in controlling the growth of crops because______
The passage suggests that which of the following is a function likely to be performed by an oligosaccharin?

选项 A、To stimulate a particular plant cell to become part of a plant’s root system
B、To stimulate the walls of a particular cell to produce other oligosaccharins
C、To activate enzymes that release specific chemical messengers from plant cell walls
D、To duplicate the gene complement in a particular plant cell
E、To produce multiple effects on a particular subsystem of plant cells

答案A

解析 The best answer is A. The last paragraph characterizes oligosaccharins as “specific chemical messengers” (lines 40-41). The passage indicates that these chemical messengers are “specific” in that, unlike the pleiotropic hormones, they are likely to have particular effects on particular plant cells. Choice A is correct because it is the only answer choice that describes an effect on a specific aspect of plant growth and development: stimulating a particular plant cell to become part of a plant’s root system. Choice B and C are incorrect because the last paragraph indicates that enzymes activate the release of oligosaccharins. Choice D is incorrect because, although oligosaccharins do affect the activity of the gene complement of a particular cell, they do not duplicate that complement. Choice E is incorrect because the second paragraph indicates that an oligosaccharin has a specific effect rather than multiple effects on plant cells.
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