单项选择题
A.a floodlight
B.two red lights in a vertical line
C.a single red light
D.any visible lights
单项选择题 At sea，you are approaching a small vessel and see that it has the signal flag P hoisted. What should you do?（）.
单项选择题 As defined in the Rules，a towing light is a yellow light having the same characteristics as a(n)（）.
单项选择题 Approaching an anchorage in fog，you hear one short，one prolonged，and one short blast in that sequence on a ship’s whistle． This indicates（）.