The correct answer is D) Slack tanks and empty tanks should be sounded. Full tanks need not be sounded. In the event of a grounding, it is important to sound the slack tanks and empty tanks to determine if there is any evidence of holing or damage to the vessel's hull. Slack tanks, which are neither full nor empty, are more likely to show signs of leakage or water ingress if the vessel has struck the bottom. Empty tanks, on the other hand, can also reveal damage that may not be visible in full tanks. Full tanks, however, are less likely to show evidence of holing and do not need to be sounded in this situation. The other answer choices are incorrect because sounding only slack tanks (A) or only empty tanks (B) would not provide a complete assessment of the vessel's condition, and sounding all tanks (C) is unnecessary and can be time-consuming.