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题库 / Prep2007E2-SC-56
Unlike crested wheatgrass, an alien species from Siberia that forms only shallow roots and produces tall above-ground shoots, native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very tall.
native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very
native North American grasses develop an extensive root system, which allows for their greater enrichment of the soil, but without growing to be that
the root system of native North American grasses is extensive, allowing for greater enrichment of the soil, but they do not grow to be very
the root system of native North American grasses is more extensive, allowing for the greater enrichment of the soil, but these grasses do not grow to be very
the extensiveness of the root system of native North American grasses allows for their greater enrichment of the soil, but they do not grow to be that
native American grasses develop a root system but do not grow tall
前面到底是develop这个动作allow还是root system这个东西allow不好确定，但but后面的grow应该和前面develop并列
A中grow和develop并列
RON:
it's the development of the extensive root system, in general, that allows for the enrichment of the soil.
to say that the grasses themselves allow for that enrichment isn't quite accurate.
allow for考虑到
but是并列连词，连接的两个部分需要平行对等
根据句首的unlike crested wheatgrass，答案剩下 choice a,b
choice a, develop & grow 是两个独立的谓语动词并列。“长出根系” 和“长得多高” 是两个没有关联的动作
choice b, but without growing to be that tall其实是一个省略后的结构，还原：but (grasses develop an extensive root system )without growing to be that tall. 这里growing作为状语修饰develop
B:but without growing在前面没有并列对象
A，but do not grow to be very tall与上一个动词develop平行，native North American grasses do not grow to be very tall
B，without可以是副词，跟在最近的动词allows后面，the root system allows for soil without growing too tall,grow的主语错误
without可以作介词，+noun构成状语，修饰最近的一个动作allows，主语还是错误
我感觉这里的but without growing to be that像是一个省略后的句子，growing修饰省略的谓语动词develop。因为如果修饰定从中的allow，grow的逻辑主语就变成了root system，但是根系是不太可能以“长得多高”来形容的。不知道对不对哈....
你这个角度理解是对的。but是并列连词，连接整个句子。当它要对连接的第二个句子做省略时，要求前一个句子有相同的成分，否则无法省略。without growing是介宾做状语，如果要省略，要求前面也带了一个状语（比如A is better now than last year，因为前面有now这个状语或者语意上能看出来指的是now，所以than后面可以只保留状语），但本题前面的句子的develop没有带状语，所以but连接的句子只保留了状语是不对的。
更正：B里的without growing做状语，没有并列对象，是but做连词的特殊用法，见“Prep2012-SC-58”。
介宾结构通常没有主语，如：“He was killed by using knife.”，不考虑without growing的主语问题。
B，enrichment of soil表示“土壤的更肥沃性”，不能带their，“草的更肥沃性”。
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but 不平行
but后要加完整句，不完整那就是省略了重复部分，未省略部分要求平行
B选项but后不是完整句子，和前面也没有可平行的，所以错
allow for 顾及到，考虑到
说的不对请大家指正。
B中的their可以refer到前面的grasses。但是它说：root system allows for greater enrichment，是整个development allow了greater enrichment，所以不是那么准确，选a。
B选项中的their用法不对