The correct answer is C) the cost of labor and material to restore the vessel to the service condition which existed before the casualty. This is the correct answer because when a vessel is involved in a casualty, the cost of property damage typically refers to the actual physical damage to the vessel and the cost to repair it. This includes the labor and materials needed to restore the vessel to its pre-casualty condition, so that it can return to service. The other options, such as lost revenue or damage claims, are not part of the property damage cost itself, but rather separate considerations. The other answer choices are incorrect because they do not directly reflect the cost of repairing the physical damage to the vessel. Option A is limited to lost revenue, while option B covers damage claims, but neither of these are the same as the actual repair costs.