15. GWD-5-Q35 to Q37白杨树为什么要惹火烧身呢 Even more than mountainside slides 即使比泥或雪滑坡多，自然发生的 of mud or snow, naturally occurring forest 山火促进白杨的生存。 fires promote the survival of aspen trees. Line Aspens’ need for fire may seem illogical 白杨对火的需要似乎不合逻辑， (5) since aspens are particularly vulnerable 因为白杨特别容易被火烧伤； to fires; whereas the bark of most trees 尽管大多数树的树皮由死细胞 consists of dead cells, the aspen’s bark 组成，白杨的树皮却是一种活 is a living, functioning tissue that—along 组织，它和其他树一样很快就 with the rest of the tree—succumbs quickly 会被烧死。 (10) to fire.提出现象 The explanation is that each aspen, 对此的解释是，每棵白杨虽然 while appearing to exist separately as 看上去单独存在，其实却仅仅 a single tree, is in fact only the stem or 是一个更大的机体的茎或苗。 shoot of a far larger organism. A group 上千株的白杨群可以构成一个 (15) of thousands of aspens can actually 单一的机体，叫克隆，它分享 constitute a single organism, called a 着互相连接的根部系统和一套 clone, that shares an interconnected root 独特的基因。 system and a unique set of genes. Thus, 所以当一棵白杨－一棵茎－死了， when one aspen—a single stem—dies, 整个克隆会受到影响。 (20) the entire clone is affected. While alive, 一棵活茎会发送荷尔蒙到根部 a stem sends hormones into the root 以压制更多的茎生长。 system to suppress formation of further stems. But when the stem dies, its 但当茎死去，荷尔蒙信号终止。 hormone signal also ceases. If a clone 如果克隆同时失去很多茎，相应 (25) loses many stems simultaneously, the 的荷尔蒙不平衡会引发巨大的 resulting hormonal imbalance triggers a 新芽的快速增长，数量比死去的 huge increase in new, rapidly growing 更多。 shoots that can outnumber the ones destroyed. An aspen grove needs to 一片白杨小林需要规律地经历 (30) experience fire or some other disturbance 火灾或其它的干扰，否则将不能 regularly, or it will fail to regenerate and 再生扩张。反过来，针叶树会侵 spread. Instead, coniferous trees will 入白杨小林的界线并日益阻挡其 invade the aspen grove’s borders and 需要的阳光。 increasingly block out sunlight needed by the aspens. 解释现象 现象解释 逻辑简图： 1P: fires promote the survival of aspen trees. Needs for fire may seems illogical…. 2P: the explanation is that… thus… -------------------------------------------------------------------------------- GWD-5-Q35: The primary purpose of the passage is to explain the
A. qualities that make a particular organism unique B. evolutionary change undergone by a particular organism C. reasons that a phenomenon benefits a particular organism D. way in which two particular organisms compete for a resource E. means by which a particular organism has been able to survive in a barren region The explanation is that each aspen, while appearing to exist separately as a single tree, is in fact only the stem or shoot of a far larger organism. -------------------------------------------------------------------------------- GWD-5-Q36: It can be inferred from the passage that when aspen groves experience a “disturbance” (line 30), such a disturbance
A. leads to a hormonal imbalance within an aspen clone B. provides soil conditions that are favorable for new shoots C. thins out aspen groves that have become overly dense D. suppresses the formation of too many new aspen stems E. protects aspen groves by primarily destroying coniferous trees rather than aspens If a clone loses many stems simultaneously, the resulting hormonal imbalance triggers a huge increase in new, rapidly growing shoots that can outnumber the ones destroyed. An aspen grove needs to experience fire or some other disturbance regularly, or it will fail to regenerate and spread. -------------------------------------------------------------------------------- GWD-5-Q37: The author of the passage refers to “the bark of most trees” (line 6) most likely in order to emphasize the
A. vulnerability of aspens to damage from fire when compared to other trees B. rapidity with which trees other than aspens succumb to destruction by fire C. relatively great degree of difficulty with which aspens catch on fire when compared to other trees D. difference in appearance between the bark of aspens and that of other trees E. benefits of fire to the survival of various types of trees
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发表于 2011-8-20 14:43:33
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