James got lost in the city, _________he had to ask for help.
A. or
B. SO
C. but
D. for
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Dogs have a very _________sense of smell.
A. nice
B. clear
C. good
D. high
There is nobody here in the office-they have all gone home.
A. can
B. must
C. should
D. would
The reason _________the president kept silent is still unknown.
A. how
B. why
C. when
D. what
Mary looks great_________ this pair of trousers.
A. in
B. by
C. on
D. at