人体缺少维生素C会患                                          ( )

A．夜盲症

B．坏血病

C．贫血症

D．佝偻病

What should you do if you have transmitted a distress call a number of times on channel 16 and have received no reply?（）

A.Repeat the message using any other channel on which you might attract attention

B.Key the microphone several times before transmitting again

C.Turn up the volume on the receiver before transmitting again

D.Report the problem to the head electrician