快考了，请教几个问题！

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.

(A) native North American grasses develop an extensive root system, allowing for greater enrichment of the soil, but do not grow to be very

(B) native North American grasses develop an extensive root system, which allows for their greater enrichment of the soil, but without growing to be that

(C) 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

(D) 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

(E) 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

Key：A

疑问，A的but后没有主语，难道是因为跟前面的主语相同，省略了？如果是这样，那42题的C选项为什么就不行呢？

42.

During the same period in which the Maya were developing a hieroglyphic system of writing, the Aztec people also developed a written language, but it was not as highly sophisticated as that of the Maya and was more pictographic in nature.

(A) but it was not as highly sophisticated as that of the Maya and was

(B) but it was not as highly sophisticated as the Maya, being

(C) but, not as highly sophisticated as the Maya's, was

(D) not as highly sophisticated as that of the Maya, however, being

(E) not as highly sophisticated as the Maya's however, it was

key:A

根据BY的总结，如果两个句子并列第一个句子含有be第二个句子的be必须省，这不是出现了违背？

非常感谢！

During the same period in which the Maya were developing a hieroglyphic system of writing, the Aztec people also developed a written language, but it was not as highly sophisticated as that of the Maya and was more pictographic in nature.

(A) but it was not as highly sophisticated as that of the Maya and was

(B) but it was not as highly sophisticated as the Maya, being

(C) but, not as highly sophisticated as the Maya's, was

(D) not as highly sophisticated as that of the Maya, however, being

(E) not as highly sophisticated as the Maya's however, it was

key:A

根据BY的总结，如果两个句子并列第一个句子含有be第二个句子的be必须省，这不是出现了违背？

非常感谢！

 not as highly sophisticated as the Maya's的主语不是the Aztec people而是a written language  所以it不能省吧