这是为什么呢?B. chores; by 1997 that figure had grown to nearly six hours a week的势态明显不对啊~~
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) "they had spent nearly six hours" distorts intended meaning, incorrectly suggesting that " children spent 6 hours at some point between 1981 and 1997."C) passive voice. D) "compared with a figure of nearly six hours a week in 1997" incorrectly modifies "chores"; incorrect.E) unidiomatic use of that.