The correct answer is A) Double luff tackle. The double luff tackle, also known as a double whip, is a type of tackle arrangement consisting of two single blocks with a rope reeved through them. This configuration provides a mechanical advantage of 2:1, meaning it takes half the force to lift a given load compared to using a single block. This makes it a suitable choice for various marine applications, such as lifting and securing heavy objects onboard a vessel. The other options are incorrect because: B) Gun tackle is a 2:1 purchase using a single and double block, C) Topping lift is a line used to raise and lower a ship's boom, and D) Three-two purchase is a 3:2 mechanical advantage system using three single blocks.