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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 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, 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.
It can be inferred from the passage that when aspen groves experience a “disturbance” (line 30), such a disturbance
E.protects aspen groves by primarily destroying coniferous trees rather than aspens
当时纠结了一下，E哪里错了？最后一句的instead 和前一句有关系吗？
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发表于 2011-8-21 12:28:52
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