问题补充：
Only at that time how much time she had wasted.
A. Mary did know
B. did Mary know
C. does Mary know
D. Mary does know
答案：
A. Mary did know
(答案→)B. did Mary know
C. does Mary know
D. Mary does know
解析：考查倒装句。Only 放在句首后接状语时，后面使用部分倒装的形式。句意：只有在那时玛丽才知道她已经浪费了多少时间。
