Mary helped Bill whenever he was in trouble but he never did anything for her _______.
A. in turn
B. in advance
C. in return
D. in vain
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The old man, _______ poor, could not afford a decent meal.
A. being
B. is
C. was
D. has been
Can you tell the _______ difference between the two words?
A. slender
B. single
C. slight
D. simple
I believe it is one of the best books _______ written on the subject.
A. that have ever been
B. which have ever been
C. that has ever been
D. which has ever been
This is a very _______ issue and we haven ’t figured out a way to deal with it yet.
A. competent
B. compound
C. comprehensive
D. complicated