GWD26-Q20

20. GWD26-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

答案：B. 请问下为什么E不可以？E的绝对性错误在哪里呢？E不可以看作一个独立主格结构吗？还是因为E本身没问题，但是把原来的by 1997变为in 1997从而改变了原句含义和侧重点（原句用过去完成时比一般过去时更强调变化）？请多多指教！

顺便想请教下：A选项的错误是因为THEY 用在这里可以特指了上一句的children（同一批人），而本来想表达的只是孩子做家务的时间，改变了意思，所以错么