Prep T2 SC Q56

[gan4sula]

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

Ans A

請問
why A is better than B?
.... system, which allows....; which -> system ? this is no better than non-restrictive ?

thank you

[dibert8]

(A) ... develop..., ..., but do not grow... 平衡; allowing 修飾主要子句
(B) but 不平衡; which = system 沒錯,不過句意改變了 (原句是 develop... 那件事 allows..., 這裡改成 system allows...); their greater enrichment 不好的表達方式 (wordy)