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 answer:B B中的时态用的不对阿，我自己选的是D，请指教！ | 
