单项选择。

— How far is it from our school to the bookshop?

— _____. [ ]

A. It isn't far.

B. It's twenty minutes.

C. It's very long.

D. It's about one kilometer.

微型机的DOS系统属于哪一类操作系统

A．单用户操作系统

B．分时操作系统

C．批处理操作系统

D．实时操作系统