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．charged

B．fined

C．free

D．controlled

集装箱货运进出口中的“谨慎放货”是指（）的操作。

A.核查与提单有关的文件

B.坚持正本提单验收

C.凭提单并交付应收费用

D.确认所有文件正确，收回正本提单后签发提货单