The correct answer is D) the ground swell making it difficult to tack off. The "lee shore" refers to the shoreline that is downwind, where the wind is blowing from the sea towards the land. In this situation, the ground swell, or waves breaking on the shore, can make it very difficult for a sailing vessel to tack, or change direction, and move away from the dangerous lee shore. This can lead to the vessel being driven onto the rocks or beach, which is the primary hazard that the old sailor's admonition warns against. The other answer choices are incorrect because they do not directly address the core issue of the ground swell hampering a vessel's ability to maneuver away from the lee shore. While factors like current, wind, and lack of wind in the lee can contribute to the overall hazardous situation, the ground swell is the primary danger described in the admonition.