The meeting was expected to start at 9 o'clock but the manager didn't turn up ______ twenty minutes later.

A．before

B．until

C．after

D．since

由楼宇自动化系统、保安自动化系统、消防自动化系统、通信自动化系统、办公自动化系统有机地联系在一起称为( )。

A．现代写字楼

B．智能化写字楼

C．管理现代化写字楼

D．智能现代化写字楼