In 1981 children in the LACE w:st="on">United StatesLACE> 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
这道题目应该选什么呢？答案是 B
但是为什么要用过去完成时呢？如果可以用过去完成时的话，A也比B好呀，对称，又是主动。 | 
