改错题 15.The root systems of most flowering perennials either become too crowded, which results in loss in vigor, and spread too far outward, producing a bare center.

A、 which results in loss in vigor, and spread
B、 resulting in loss in vigor, or spreading
C、 with the result of loss of vigor, or spreading
D、 resulting in loss of vigor, or spread
E、 with a resulting loss of vigor, and spread

【正确答案】 D

【答案解析】Idiom; Parallelism
This sentence uses the construction either x or y, x and y must be grammatically parallel. In this case, and spread must be or spread. The antecedent of which is unclear; replacing which results with resulting clarifies the meaning.
A Either is incorrectly followed by and; which has no clear referent.
B Or spreading is not parallel to either become.
C With the result of is wordy and awkward. Or spreading is not parallel to either become.
D Correct. The phrase resulting in loss of vigor concisely modifies the first clause; the either/or construction is correct and parallel in this sentence.
E Either is incorrectly followed by and; with a resulting loss is wordy.
The correct answer is D.