They found it difficult ____ the task in such a short time.
A. finishing
B. to finish
C. finished
D. to have finished
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It is against my principles _____ with them.
A. to collaborate
B. collaborating
C. collaborated
D. to be collaborated
There're so many kinds of tape-recorders on sale that I can't make up my mind _ to buy.
A. what
B. which
C. how
D. where
-Have you decided when _____?- Yes, tomorrow morning
A. to leave
B. to be leaving
C. will you leave
D. are you leaving
He doesn't know _______ to stay or not.
A. whether
B. if
C. either
D. if he will
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