Expired / Rules of the Road: BOTH INTERNATIONAL & INLAND Which signal may at some time be exhibited by a vess...

I don't get this answer... A: Could be if the vessel is aground or not under command, but the question says she is trawling, if the vessel is aground or not under command then how can she be trawling; B: hmmm a Pilot Vessel engaged in Trawling? C: The vessel is trawling not towing; Maybe D should be "none of the above"? or am I completely missing something here.