单项选择题
A.painted red and labeled
B.concealed from the crew
C.protected by plexiglass
D.padlocked
单项选择题 The sign used to caution persons approaching the gangway of a tank barge during cargo transfer reads（）.
单项选择题 What is not accepted as the required shipping paperson a manned and loaded tank barge?（）.
单项选择题 What will be accepted as the shipping papers for an unmanned tank barge but will not be accepted if the tank barge is manned?（）.