He has been in bed ______ he fell off his bike a week ago.             

A．even if

B．soon after

C．now that

D．ever since

（）是从数控装置中发出的脉冲序列，每个脉冲与机床单位位移量相对应，而构成指令。

A.程序

B.指令脉冲

C.顺序控制