问题
单项选择题
Packet-switching wireless networks are preferable (41) when transmissions are (42) because of the way charges are (43) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (44) for the (45) of time they use the net-work.
A．long
B．short
C．large
D．small
答案
参考答案：B