规定自负极通过电源内部指向正极的方向为电动势的方向。( )
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A robot ___ think for itself. It must be told what to do.
A. can't
B. couldn't
C. may not
D. might not
Let's go on a picnic, ___?
A. shall we
B. will you
C. may we
D. could you
You ___ carry the luggage for me, for I only have one bag.
A. needn't
B. can't
C. mustn't
D. wouldn't
"___ he use your bike now?""Certainly. Here is the key.
A. Does
B. Must
C. Shall
D. Will