单项选择题

A yellow signal，floating in the air from a parachute，about 300 feet above the water，indicates that a submarine（）.

A.will be coming to periscope depth
B.will be coming to the surface
C.is on the bottom in distress
D.is in distress and will try to surface

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单项选择题

A.pulling a submarine cable
B.engaged in diving operations
C.engaged in underway replenishment
D.transferring explosives

单项选择题

A.identity
B.time of origin
C.reply
D.procedure code

单项选择题

A.reply
B.text
C.time
D.answer