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．long

B．short

C．large

D．small

患儿，男，8岁，突发剑突下阵发性钻顶样剧痛，超声探查发现胆囊内长条形双线状回声。超声诊断为（）。

A.胆囊炎

B.胆囊蛔虫症

C.胆囊癌

D.化脓性胆管炎

E.胆结石