采用高频开关型整流器的局（站），应按（）冗余方式确定整流器配置，其中n只主用，n≤10时，1只备用；n＞10时，每10只备用1只。

A.n

B.n+1

C.n+2

D.n+3

Which signal is recognized as a distress signal?（）

A.Directing the beam of a searchlight at another vessel

B.A smoke signal giving off orange colored smoke

C.A whistle signal of one prolonged and three short blasts

D.International Code Signal "PAN" spoken over the radiotelephone