问题补充：
How time flies!Its already twelve oclock.
Oh,really? I it at all.
A. don realize
B. didn realize
C. haven realized
D. hadn realized
答案：
A. don realize
(答案→)B. didn realize
C. haven realized
D. hadn realized
解析：句意：时间过得真的快！现在已经12点了。哦，真的吗？我一点都没有注意到。realize意识，表示过去的动词，说明过去没有意识到这样，故用一般过去时即可，故选B
