Which statement is TRUE concerning spare charges for portable fire extinguishers on unmanned tank barges?（）.
A.Spare charges shall be carried for at least 50 percent of each size and variety required on board
B.If the unit cannot be charged by the vessel's personnel，one spare unit shall be carried in lieu of spare charges
C.Spare charges shall be stowed in watertight containers on deck
D.Regulations concerning spare charges do not apply to unmanned barges