A distress signal（）.

A.consists of 5 or more short blasts of the fog signal apparatus
B.consists of the raising and lowering of a large white flag
C.may be used separately or with other distress signals
D.is used to indicate doubt about another vessel's intentions

A.Abandon vessel
B.Adrift
C.Beach to
D.Assembly station

A.displaying a large red flag
B.displaying three black balls in a vertical line
C.sounding four or more short rapid blasts on the whistle
D.continuously sounding the fog whistle