We arrive ___________ Nanjing on Monday.[ ]
A. at
B. on
C. in
D. of
答案：C
哥伦比亚广播公司Columbia Broadcasting System）
IP multicasting is a set of technologies that enable efficient delivery of data to manylocations on a network．Rather than making multiple copies of a message intended to bedistributed to multiple recipients at the (71) of origin of a message，multicasting initiallysends just one (72) and does not copy it to the individual recipients until it reaches theclosest common point on the network，thereby (73) the bandwidth consumed．Networkperformance is significantly (74) because it isn’t bogged down with the processing andtransmission of several large data files；each receiving computer doesn’t have to (75) thetransmitting server for the file．
A．dropped B．proved C．improved D．upgraded
