A clean ballast tank is one which

A. Is not allowed to carry any oil cargo and solely to be used for the purpose of carriage of ballast water
B. Is used for the carriage of oil cargo, but has to be cleaned thoroughly prior carriage of ballast water during ballast voyage
C. Is allowed to carry some white and clean oil cargoes and has to be cleaned up thoroughly for the carriage of ballast water
D. Is a tank which was previously being used for the carriage of oil cargo, but was converted to a ballast tank during last dry-docking, but still has a common pumping system for remaining cargo tanks and the converted clean ballast tank