文化基础学科的作业可分为（）

A．课内作业和课外作业

B．独立完成作业和合作完成作业

C．语文作业和数学作业

D．知识作业和应用作业

Packet-switching wireless networks are preferable (71) when transmissions are (72) because of the way charges are (73) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (74) for the (75) of time they use the network.

A．to

B．for

C．than

D．only