电磁机构中衔铁可靠地被吸住的条件是（）
A、电磁吸力大于弹簧反力
B、电磁吸力等于弹簧反力
C、电磁吸力小于弹簧反力
参考答案：A
The students haven't finished their homework, _____?[ ]
A. do they
B. don't they
C. have they
D. haven't they
将购进药品销售给消费者的药品经营企业是( )
A．新药B．药品经营方式C．药品经营范围D．药品批发企业E．药品零售企业
