“Not having returned home yet, _________”, his father said to the police.

A．his mother got worried

B．his mother must be worried

C．I think he is missing

D．he must have got into some trouble.

下列不属于机械工业的是[ ]

A．轮船制造

B．纺纱织布

C．机床制造

D．拖拉机制造