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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
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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