SC - 1981

Can someone please explain me what is wrong with A?
the correct answer is B. however, don't we lose the meaning of the sentence when we bring new verb "had grown" ?

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,
...

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