“网站提供给用户发布信息的工具，往往作为一项服务于网站相应的发布空间相联系”，这句话描述的网上单证是（）。

A.分注册类网上单证

B.息发布类网上单证

C.通信息交流类网上单证

D.业商务操作类网上单证

IP multicasting is a set of technologies that enable efficient delivery of data to many locations on a network. Rather than making multiple copies of a message intended to be distributed to multiple recipients at the (71) of origin of a message, multicasting initially sends just one (72) and does not copy it to the individual recipients until it reaches the closest common point on the network, thereby (73) the bandwidth consumed. Network performance is significantly (74) because it isn’t bogged down with the processing and transmission of several large data fries; each receiving computer doesn’t have to (75) the transmitting server for the file.

A．point

B．bottom

C．head

D．sight