A.allow sufficient oxygen in the tank to sustain life
B.prevent outside air from entering the tank
C.provide more discharge pressure
D.comply with pollution regulations

A.displayed in at least 4 different positions on the barge
B.carved on a wooden board and attached to the barge's hull
C.displayed as close to the navigation lights as possible
D.displayed at the highest point of the barge's hull such that it can be seen from either side