I must be off now, ______I' be late for the meeting.
A. but
B. and
C. for
D. or
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β-受体兴奋剂,能扩张血管,但容易诱发心动过速者是指E.
The purpose of the new economic policy is not to hinder economic growth______ to guide it
A. and
B. as
C. but
D. nor
My car is always breaking down, but I don't know enough about ______ to be able to fix it
A. mechanics
B. mechanism
C. mechanic
D. medicine