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B,为什么A 不行

A中的they指代81年的children，但是1997，他们已经不是children了。

指代错误。