A vessel,which does not normally engage in towing operations,is towing a vessel in distress.She ____.
A.need not show the lights for a vessel engaged in towing,if it is impractical to do so
B.may show the lights for a vessel not under command
C.must show a yellow light above the stern light
D.must show the lights for a vessel towing
请帮忙给出正确答案和分析,谢谢!