单项选择题
A.red lights
B.red lights and two white lights
C.red lights with a white light in between
D.white lights with a red light in between
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（）.
单项选择题 A vessel，which does not normally engage in towing operations，is towing a vessel in distress.She（）.
单项选择题 A vessel sounding a fog signal of one short，one prolonged，and one short blast is indicating that the vessel is（）.