The correct answer is B) Threefold purchase. The threefold purchase, also known as a triple purchase, is a type of tackle arrangement commonly used on vessels to provide a mechanical advantage for hoisting or lifting heavy loads. This arrangement consists of three parts or "falls" running through a set of blocks, which multiplies the force applied to the tackle, making it easier to lift the load. The other answer choices are incorrect because: A) Clew garnet tackle is a different type of purchase used for securing and adjusting the clew of a sail. C) Boat falls refer to the ropes used to lower and raise a boat that is suspended from a ship's davits. D) A triple purchase is the same as a threefold purchase, so this is a redundant answer.