No agreement has been reached as both sides refused to ________ at the meeting held yesterday evening.

A．give out

B．give in

C．give up

D．give off

下列系统中，( )是实时系统。

A．计算机激光照排系统

B．航空订票系统

C．办公自动化系统

D．计算机辅助设计系统