GWD26-Q20

In 1981 children in the United States spent an average of slightly less than two and a half hours a week doing household chores; by 1997 they had spent nearly six hours a week.

A.    chores; by 1997 they had spent nearly six hours a week

B.    chores; by 1997 that figure had grown to nearly six hours a week

C.    chores, whereas nearly six hours a week were spent in 1997

D.    chores, compared with a figure of nearly six hours a week in 1997

E.    chores, that figure growing to nearly six hours a week in 1997

答案是B,  B里面用了过去完成时,这令我完全无法理解

我自己则在C和E里面举棋不定,求教大家!

CDE看到in 1997就排除了。by 1997指1981-1997这个时间段，也解释了为什么用过去完成时。in 1997把原文意思都改变了。

即是说CDE的错误在于改变原意, 明白了,多谢!!!!