242. You are towing a 1000 gross ton gasoline tank barge. Regulations say that cargo tank hatches, ullage holes, and Butterworth plates may remain open without flame screens ONLY __________.

A. if the barge is towed on a hawser astern
B. if an approved type B-II fire extinguisher is provided
C. when the open tanks are gas free
D. for periods not to exceed five minutes