The correct answer is D) All of the above. All types of lashing gear used aboard Ro-Ro (roll-on/roll-off) vessels, including wire rope, webbing, and chain, should be properly maintained when not in use. This is in accordance with industry standards and safety regulations to ensure the integrity and functionality of the lashing equipment. Proper maintenance helps prevent damage, wear, and deterioration, which is critical for securing cargo and preventing accidents aboard Ro-Ro vessels. The other options, A, B, and C, are incorrect because they would only address one type of lashing gear, when all types require proper maintenance when not in use.