The correct answer is B) 000 ft-long tons. The lightweight transverse free surface moments are zero (000 ft-long tons) when the tank is full or empty, as there is no free surface effect. Free surface effects only become relevant when the tank is partially filled, which can affect the vessel's stability. Since the question does not provide any information about the tank filling level, the default lightweight transverse free surface moment is 000 ft-long tons. The other options are incorrect because: A) 680,914 ft-long tons is an unrealistic value not based on standard regulations. C) -5,937 ft-long tons and D) -6,716 ft-long tons are negative values, which would imply the free surface effect is destabilizing, which is not the case when the tank is full or empty.