Why the explosion occurred was ____the laboratory attendant had been careless.
The old man _______ up late,but now he _________ up early.
Pointing to the house on ____ roof grew lots of bush, the old man told me that was where I would stay.
There are cases _____ the word “school”is used as a verb(动词).
In the dark street, he could find nobody he could ______.
The robber would ____ to 7 years in _____ prison.