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【单选题】
滴定分析中,一般用指示剂颜色突变来判断滴定是否停止。则指示剂变色时停止滴定的那一点称为A.
化学计量点
B.
滴定误差
C.
滴定终点
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举一反三
【单选题】We are told everywhere. It's our duty to keep our school clean and tidy. [ ]
A.
not to make much noise
B.
to throw waster paper
C.
to draw
D.
not to spit
【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】In class, Miss Zhang is really __ about our study. But after class, she always tries many ways to make our school life not so boring.
A.
serious
B.
hard-working
C.
surprised
【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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