A.at current price at the nearest main bunkering port
B.at current price at the port of redelivery if it is not available to obtain the current price at the nearest main bunkering port
C.at current price at the nearest main bunkering port if it is cheaper than that at the port of redelivery
D.at current price at the port of redelivery if it is obtainable,even the price is higher at the nearest main bunkering port