单项选择题
An inconspicuous，partly submerged vessel or object being towed，where the length of tow is 100 meters，shall show（）.
A.yellow lights at each end B.two red lights in a vertical line C.a black ball D.a diamond shape
单项选择题 An all-round flashing yellow light may be exhibited by a(n)（）.
单项选择题 All fog signals shall be sounded every two minutes with the exception of a vessel（）.
单项选择题 According to the Rules，when should lights be displayed?（）.
