GWD一道语法题求教

Irene1221

20. GWD26-Q20 (B)
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

这道题答案选B, 我没有问题，但A, C, D也没有明显的语法错误啊？是语义问题吧？求大师指点，谢谢。

Fiona09

传送给楼主Helr大神的解释：https://gmat.la/question/GMATLA-SC-84

Irene1221

谢谢，明白了。