The correct answer is D) 4. The mechanical advantage of a tackle, also known as a block and tackle system, is determined by the number of rope parts supporting the load. In the illustration D029DG, the tackle system shown has 9 parts of rope supporting the load, which means the mechanical advantage is 4. The other answer choices are incorrect because: A) 1 is too low for a 9-part tackle system. B) 2 is too low for a 9-part tackle system. C) 3 is too low for a 9-part tackle system.