对整修中检测出有轻微缺陷的转辙机底壳，如（）、（）等，在不影响设备正常使用和机械强度的情况下，可作焊接处理。
参考答案：裂纹；破损
— It's said a pianist will perform at Poly Theater on Friday evening. Is it Lang Lang?
— Yes, it _______ him. He _______ for a week.
A．must be; has arrived here
B．Can’t; has been here
C．must be; has been here
D．maybe; has arrived here
外部时滞可以分为（）两个阶段。
A.微观决策时滞和作用时滞
B.行动时滞和微观决策时滞
C.作用时滞和行动时滞
D.内部时滞和中间时滞
