中国终于有了自制的航空母舰,这确实值得骄傲。
China has owned its first homemade aircraft carrier finally. That's really something to be ____ ____.
如图所示,竖直平面内边长为a的正方形ABCD是磁场的分界线,在正方形的四周及正方形区域内存在方向相反、磁感应强度的大小均为B的与竖直平面垂直的匀强磁场,M、N分别是边AD、BC的中点.现有一质量为m、电荷量为q的带正电粒子从M点沿MN方向射出,带电粒子的重力不计.
将一个直角三角板绕直角边旋转一周,则旋转后所得几何体是( )
—Have you ever _______ to bring your homework to school?
—Yes. I _______ it at home once last term.