The correct answer is A) slacking the tripping line and towing the sea anchor by the holding line. When landing stern first in heavy surf, slacking the tripping line and towing the sea anchor by the holding line allows the sea anchor to check the sternway (backward movement) of the vessel. This method enables the sea anchor to act as a drag and slow down the vessel's backward motion, helping to maintain control and prevent the stern from being driven forcefully into the surf. The other options are incorrect because B) towing the apex end forward with the tripping line would not check the sternway, C) slacking the tripping line and towing the sea anchor from the stern would not effectively check the sternway, and D) towing with the tripping line and leaving the holding line slack would not provide the necessary drag to control the sternway.