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发布时间：2006-06-22 13:28     点击：

    (E) despotism: arrogant

    16. FLOUT: DISREGARD::

    (A) taunt: challenge

    (B) protest: overrule

    (C) revolt: secede

    (D) clamor: argue

    (E) harass: badger

    Although pathogenic organisms constantly alight on the skin, they find it a very unfavor- able environment and, in the absence of injury, have great difficulty colonizing it. This "self- (5) sterilizing" capacity of the skin results from the tendency of all well-developed ecosystems toward homeostasis, or the maintenance of the status quo.

    Species that typically live in soil water, and (10)elsewhere rarely multiply on the skin. Un- damaged skin is also unfavorable to most human pathogens. The skin is too acid and too arid for some species. The constant shedding of the surface skin layers further hinders the establishment of invaders. The most interesting (15)defense mechanism, however, results from the metabolic activities of the resident flora. Unsaturated fatty acids, an important com- ponent of the lipids in sebum collected from the skin surface inhibit the growth of several bac- (20)terial and fungal cutaneous pathogens. These acids are a metabolic product of certain gram- positive members of the cutaneous community, which break down the more complex lipids in freshly secreted sebum.

    17. The primary purpose of the passage is to

    (A) offer an analysis of metabolic processes

    (B) detail the ways in which bacteria and fungi can be inhibited

    (C) describe mechanisms by which the skin protects itself against pathogens

    (D) analyze the methods whereby biological systems maintain the status quo

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