A:尊老爱幼
B:自立自强
C:诚实守信
D:艰苦奋斗
电视机显像管简单原理如图所示,初速度不计的电子经加速电场加速后进入有限边界宽度为L的匀强磁场,磁感应强度为B,如要求电子束偏转角为α,已知电子电量为e,质量为m.
At the beginning of the 20th century, many people thought that the family was falling apart—__________, they thought it was dying. ( )