（1）     GWD-26-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

A有什么问题吗。答案为B

是否A中they 指代有问题，请高人指点

A的意思好象是有问题的

到了1997年，他们已经每周花了六小时

相反，B的意思就没什么问题

到了1997年，这个数字已经达到了每周六小时

这个题时态好奇怪，为什么1981年 spent

1997年had done