The correct answer is A) secured or stowed out of the way. When not in use, lines or gear should be properly secured or stowed away to avoid creating tripping hazards or obstructions on the deck. This is a key safety requirement to maintain clear and unobstructed walkways on a vessel. Leaving lines or gear lying about on the deck (option B) or stowing them anywhere (option C) would be unsafe and against standard maritime practices. Conspicuously marking unused lines or gear (option D) is not sufficient - they should be properly secured or stowed.