At Reference. In flight, with centre tank empty and APU operating, a fuel unbalance is detected (quantity in tank 1 < quantity in tank 2).
Rebalancing of the two tanks is:
Aimpossible without causing the APU stop.
Bpossible with "CROSSFEED" open and tank 2 pumps "OFF".
Cpossible with "CROSSFEED" open and tank 1 pumps "OFF" and tank 2 pumps "ON".
Dimpossible because there is no fuel in center tank.