_____ you know English is important, you should learn it well.
解决西北地区发展农业缺水问题,最有效的措施是( )
如图所示,两轻质闭合金属圆环,穿挂在一根光滑水平绝缘直杆上,原来处于静止状态.当条形磁铁的N极自右向左插入圆环时,两环的运动情况是( )
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