构成计算机电子的或机械的物理实体被称为( )。

A．主机

B．外设

C．计算机系统

D．计算机硬件系统

When does a pilot say make all lines fast ? He says it when（）.

A.the ship is very close to the pier

B.the ship is about to be in position

C.the ship is in position

D.the ship is getting alongside the pier