以下选项中，属于广域网的是________。
A．宿舍网
B．国家网
C．校园网
D．楼宇网
参考答案：B
28．The largest collection ever found in England was one of about 200,000 silver coins, _____ over 600 years old．
A．all of which
B．all of it
C．all of that
D．all of them
强心苷中毒引起的窦性心动过缓可选用（）
A.氯化钾
B.阿托品
C.利多卡因
D.肾上腺素
E.吗啡
