The emergency signal for fires is sounded on the ship’s whistle and general alarm as（）.

A.a continuous ringing for 10 seconds

B.one short ring followed by one long ring

C.two long rings of at least 20 seconds

D.a continuous ringing until the fire is extinguished

节假日和重要通信期要加强通信值班和机房巡视，节前应进行网络和机房安全检查后进行封网，封网期间禁止（）、各类割接和局数据的变动。

A、机房清洁

B、上级部门检查

C、参观

D、工程施工