Packet-switching wireless networks are preferable (1) when transmissions are (2) because of the way charges are (3) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (4) for the (5) of time they use the network.

1（）

A．to

B．for

C．than

D．only

"窥一斑而见全豹"，这符合知觉的（）

A.选择性

B.理解性

C.整体性

D.恒常性