如图所示，ab，cd为铁棒，当电键S闭合后，ab，cd就被磁化，磁化

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问题选择题

如图所示，ab，cd为铁棒，当电键S闭合后，ab，cd就被磁化，磁化后的极性为

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A．a端为N极，d端为N极　

B．a端为S极，d端为S极

C．b端为S极，d端为S极　　

D．b端为N极，d端为N极

答案

答案：B

单项选择题

不属于动植物检验检疫范围的有：( )

A．进出境的动植物及其产品和其他检疫物；

B．来自动植物疫区的运输工具；

C．进境拆卸的废旧船只。

D．以上都不是

选择题

33. Only when ____in the afternoon _____able to leave.

A．the match was over; they were

B．was the match over; were they

C．was the match over; they were

D．the match was over; were they