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.
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
1.其实这道题的1981 是个无关量 the only relevant places on the proverbial timeline are :(a) when the number of hours started growing (this is the 'earlier event' or FIRST time marker)(b)1997 (the SECOND past time marker). because 1997 is in the past, and the 'arrow of relevance' points to / stops at 1997 所以选择过去完成时 BY可以看出来 如果换成现在的统计数据代替的话 ("as of today, the number has grown to..."), 就用现在完成时 2.A中的they没有指代对象