He has been out of work for three months; as a result, he has to ____on family expenses by one-third.

A．cut out

B．cut down

C．cut up

D．cut off

在下列操作系统的各个功能组成部分中，哪一个不需要硬件的支持

A．进程调度

B．时钟管理

C．地址映射

D．中断系统