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Q35 to Q37:
Even more than mountainside slides
of mud or snow, naturally occurring forest
fires promote the survival of aspen trees.
Line Aspens’ need for fire may seem illogical
(5) since aspens are particularly vulnerable
to fires; whereas the bark of most trees
consists of dead cells, the aspen’s bark
is a living, functioning tissue that—along
with the rest of the tree—succumbs quickly
(10) to fire.
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. A group
(15) of thousands of aspens can actually
constitute a single organism, called a
clone, that shares an interconnected root
system and a unique set of genes. Thus,
when one aspen—a single stem—dies,
(20) the entire clone is affected. While alive,
a stem sends hormones into the root
system to suppress formation of further
stems. But when the stem dies, its
hormone signal also ceases. If a clone
(25) 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
(30) experience fire or some other disturbance
regularly, or it will fail to regenerate and
spread. Instead, coniferous trees will
invade the aspen grove’s borders and
increasingly block out sunlight needed by
the aspens.
Q36:
It can be inferred from the passage that when aspen groves experience a “disturbance” (line 30), such a disturbance
leads to a hormonal imbalance within an aspen clone
provides soil conditions that are favorable for new shoots
thins out aspen groves that have become overly dense
suppresses the formation of too many new aspen stems
protects aspen groves by primarily destroying coniferous trees rather than aspens
这题的参考答案是A，不过偶对A有疑惑。偶对文章的理解是Because the stem of aspen dies, its hormone signal also ceasese...The resulting homonal imbalance triggers a lhuge increase in new, rapadily growing shoots than can outnumber the ones destroyed(文中第24-33行).因此推出aspen 需要用火或者其它的干扰来解决这个现象。所以hormone的不均衡是因，干扰是果。根据A答案，干扰是因，hermone不均是果。另外一个证据是，第31行，如果aspen不能被定期干扰一下，它就不能再生或是扩张。这符合C说的干扰会清理掉过密的aspen groves. 请NN们指点一下，是我理解错了? 我是选C。 | 
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发表于 2004-9-23 04:23:00
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