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．computing

B．incurious

C．incurved

D．incurred

乳腺X线摄影系统性能的总体要求应具备的特点有（）。

A.高对比度

B.高分辨力

C.低剂量

D.高密度分辨力

E.高空间分辨力