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