The number of historic buildings which ________ has reached a surprising figure that we must be aware of.

A．has been pulled down

B．had been pulled down

C．is being pulled down

D．have been pulled down

可以实现身处异地的招标单位、投标单位面对面沟通的采购信息技术是( )。

A．计算机网络系统

B．Interner网络

C．专用软件

D．远程视讯系统