97.(29753-!-item-!-188;#058&003991)
Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time they have introduced some 100,000 dangerous chemical pollutants, having gone virtually unregulated since they were developed more than 50 years ago.
(A) while at the same time they have introduced some 100,000 dangerous chemical pollutants, having
(B) while at the same time introducing some 100,000 dangerous chemical pollutants that have
(C) while they have introduced some 100,000 dangerous chemical pollutants at the same time, which have
(D) but introducing some 100,000 dangerous chemical pollutants at the same time that have
(E) but at the same time introducing some 100,000 dangerous chemical pollutants, having
答案是B可以理解,只是这里我想提一个问题。
在主句里的时态是have improved现在完成时,用while引导的从句表示同时发生,自然应该和主句保持平行,也使用现在完成时,可是B里while introducinng明显是while they are introducing的省略,因为只有存在系动词的时候while才可能省略主语,这里不就和主句完成时态不平行了吗? |