Though I was tired out that evening, I _____ from falling asleep by the great pain in my knee. 
#100941
A
was prevented
B
had prevented
C
has prevented
D
am prevented
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  I have no idea what _____ while I was asleep.
#100185
A
has happened
B
could happen
C
had happened
D
happened
--Why has he been staying at home these days?  --He ___________ since a month ago.
#104803
A
has been out of work
B
was out of work
C
has lost his work
D
had left from his work