The correct answer is C) idling gears rotate in a direction opposite to their rotation when carrying load. In a reversing reduction gear, the forward and reverse main pinions are in constant mesh with the main gear. This means that when the main gear is rotating, the forward and reverse pinions will also be rotating, even if they are not actively driving the system. When the pinions are idling (not clutched in), they will rotate in the opposite direction of their normal rotation when they are actively driving the system. This is a fundamental characteristic of the design of a reversing reduction gear. The other answer choices are incorrect because they do not accurately describe the behavior of the idling gears in a reversing reduction gear system.