A:1个
B:2个
C:3个
D:4个
— You should write a passage in the English exam.
— I think it's not difficult for us to write if you try your best.
一个茶杯高约( )
—Is Ann your sister?
—__________. She is my friend.
带电粒子A的质量为m,电量为q。带电粒子B的质量为4m,电量为2q。两个粒子分别以相同速度垂直磁感线射入同一匀强磁场中(不计带电粒子的重力)。则两粒子做圆周运动的半径之比R a∶Rb=____,周期之比T a∶Tb=____。