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 author mentions specific effects that auxin has on plant development in order to illustrate the______

选项 A、point that some of the effects of plant hormones can be harmful
B、way in which hormones are produced by plants
C、hierarchical nature of the functioning of plant hormones
D、differences among the best-known plant hormones
E、concept of pleiotropy as it is exhibited by plant hormones

答案E

解析 The best answer is E. The second paragraph states that the five major plant hormones, including auxin, are pleiotropic and indicates that each pleiotropic hormone has “more than one effect on the growth and development of plants” (lines 15-16). The effects of auxin are then listed in detail to provide an example of the different effects a pleiotropic hormone can have on a plant. Thus, the specific effects of auxin are mentioned to illustrate the concept of peiotropy as it is exhibited by plant hormones. Choice C can be eliminated because the specific effects that auxin has on plant development are not discussed in the context of the hierarchy of hormones. Choice A, B, and D are incorrect because they cite topics that are nor discussed in the passage.
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