130-60=____
300+30=____
300+300=____
60+90=____
— Well, it's hard to say, probably great, or maybe not.
魏格纳是从哪两个大洲的轮廓吻合提出大陆漂移学说的( )
如图所示,框架面积为S,框架平面与磁感应强度为B的匀强磁场方向垂直,则穿过平面的磁通量为____.若使框架绕OO′转过60°角,则穿过框架平面的磁通量为____.