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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
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
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