一平行板电容器,两板相距为d,与一电池联接时,相互作用力为f。若将电池断开,把距离拉到3d,则相互作用力变为:( )。
A. f/3;
B. 3f;
C. 9/f;
D. 不变。
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Maths, one of the most important subjects, ______always interested him.
A. has
B. have
C. are
D. is
I’m Chinese. Where______from?
A. do you come
B. you are coming
C. you come
D. are you coming
May______to school.
A. never walks
B. is never walking
C. walk never
D. never is walking
We will start as soon as our teacher______ .
A. comes
B. will come
C. come
D. is coming
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