----- An explosion at a coal mine of Panzhihua killed at least 43 workers and left another 3 missing.

-------Yes,_______ news came as _______ shock to us all.

A．the; the

B．/ ; /

C．/ ; a

D．the; a

采用直接交换方式的 Ethernet 交换机，其优点是交换延迟时间短，不足之处是缺乏______。

A．并发交换能力

B．差错检测能力

C．路由能力

D．地址解析能力