In 1981 children in the United States spent an average of slightly less than two and a half hours a weekdoing household chores; by1997 they had spent nearly six hours a week.
A. chores; by 1997 they hadspent nearly six hoursa week
B. chores; by 1997 thatfigure had grown to nearlysix hours aweek
C. chores, whereas nearlysix hours a week were spent in 1997
D. chores, compared with afigure of nearly six hours a week in 1997
E. chores, that figuregrowing to nearly six hours a week in 1997
选B。想请问一下,C答案错在哪里了呢?wheres不是说不需要结构对称,我不选B是因为觉得后面用过去完成式不对。前面1981只用了过去式,而1997却用过去完成式??难道1997比1981还早?所以我就觉得不应该是过去完成式。请大牛指教一下。为什么这里是可以使用过去完成时,还有应该再什么情况下能用过去完成时。谢谢拉
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