Congratulations to nostr:npub1cppnptddm9ggcxk3cmk7ptk4my32xetsyxfhugz44qxpk2r9enmszgyqlx for solving the puzzle! Here's the answer:

A: The man filled the jug with water from the ocean. He arranged the plank on the ground and poured water into its shadow, which refracted the lantern light into an SOS pattern, which was seen by the passing ship at night.

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