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美国GRE出国考试模拟试题13

时间:2011-09-29来源:作文地带栏目:Essay作者:作文地带整理 英语作文收藏:收藏本文
作文地带导读:quite consistent with the wind dispersal of pollen, clouds of which are released from some of the larger cones.about cycad pollination and what the structure of most female cones suggests about that process.
作文地带导读:quite consistent with the wind dispersal of pollen, clouds of which are released from some of the larger cones.about cycad pollination and what the structure of most female cones suggests about that process.

  美国GRE出国考试模拟试题13

  Experiments show that insects can function as pollinators

  of cycads, rare, palmlike tropical plants. Furthermore, cycads

  removed from their native habitats—and therefore from

  insects native to those habitats—are usually infertile. Nev-

  (5) ertheless, anecdotal reports of wind pollination in cycads

  cannot be ignored. The structure of cycads male cones is

  quite consistent with the wind dispersal of pollen, clouds

  of which are released from some of the larger cones. The

  male cone of Cycas circinalis, for example, sheds almost

  (10)100 cubic centimeters of pollen, most of which is probably

  dispersed by wind. Still, many male cycad cones are com-

  paratively small and thus produce far less pollen. Further-

  more, the structure of most female cycad cones seems incon-

  sistent with direct pollination by wind. Only in the Cycas

  (15)genus are the females’ ovules accessible to airborne pollen,

  since only in this genus are the ovules surrounded by a

  loose ag美国GREgation of megasporophylls rather than by a tight

  cone.

 

  24.According to the passage, the size of a male cycad

  cone directly influences which of the following?

  (A) The arrangement of the male cone’s structural

  elements

  (B) The mechanism by which pollen is released from

  the male cone.

  (C) The de美国GREe to which the ovules of female cycads

  are accessible to airborne pollen

  (D) The male cone’s attractiveness to potential insect

  pollinators

  (E) The amount of pollen produced by the male cone

 

  25. The passage suggests that which of the following is

  true of the structure of cycad cones?

  (A) The structure of cycad cones provides conclusive

  evidence in favor of one particular explanation

  of cycad pollination.

  (B) The structure of cycad cones provides evidence

  concerning what triggers the first step in the

  pollination process.

  (C) An irresolvable discrepancy exists between what

  the structure of most male cycad cones suggests

  about cycad pollination and what the structure of

  most female cones suggests about that process.

  (D) The structure of male cycad cones rules out a

  possible mechanism for cycad pollination that is

  suggested by the structure of most female cycad

  cones.

  (E) The structure of male cycad cones is consistent

  with a certain means of cycad pollination, but

  that means is inconsistent with the structure of英语作文
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