解决最小枝杈树问题,在国外一般应用普莱姆法或()两种方法。
参考答案:克鲁斯喀尔法
质量为m的通电细杆ab置于倾角为θ的导轨上导轨宽度为d,杆ab与导轨间的动摩擦因素为μ,有电流时,ab恰好在导轨上静止,如图甲所示,它的四个侧视图中表示出四种可能的匀强磁场方向,如图乙所示,其中杆ab与导轨之间的摩擦力可能为零的图是()
George is going to talk about the geography of his country,but I'd rather he_____ more on its culture.[ ]
A.focus
B.focused
C.would focus
D.had focused