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【多选题】
以下不是狄拉克预言的粒子有()A.
α粒子
B.
β粒子
C.
γ粒子
D.
反粒子
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皮皮学刷刷变学霸
举一反三
【单选题】To make our school more beautiful, rubbish into the river.
A.
can’t throw
B.
mustn’t be thrown
C.
needn’t be thrown
D.
shouldn't throw
【单选题】Trees and flowers _____ every year to make our school more beautiful. A. plant B. are planted C. were planted
A.
plant
B.
are planted
C.
were planted
【单选题】We must try our best to make our school more beautiful and ___ noisy.
A.
little
B.
less
C.
much
D.
more
【单选题】_______ has been done to make our school more beautiful.
A.
Many
B.
Much
C.
A lot of
D.
A few
【单选题】To make our school beautiful, we _____ throw rubbish here and there.
A.
needn’t
B.
must
C.
need
D.
mustn’t
【多选题】关于直流电动机，下列叙述正确的是 [ ]
A.
直流电动机的原理是电流的磁效应
B.
直流电动机正常工作时，是将电能转化为机械能
C.
直流电动机的换向器是由两个彼此绝缘的铜制半环组成的
D.
电源的正负极和磁场的方向同时改变，直流电动机的转动方向也改变
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