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

定量测定17-羟、17-酮时，选用的防腐剂是

A．甲醛
B．甲苯
C．浓盐酸
D．麝香草酚
E．碳酸钠