There are 2 different types of ice protection systems, de-icing systems and anti-icing systems. They are quite simple to remember, de-icing is the process of getting rid of the ice that has already formed, whereas anti-icing is preventing the ice from forming at all.

The different parts of the aircraft that require ice protection are the wing leading edges, the tail leading edges, any probes or vanes, the windscreen, the engine inlets and the propellers (if fitted). All these components can be de-iced when ice is detected, except for the engines, which have to be anti-iced, as any ice build up could fall into the engine when dislodged and potentially cause a flame out or even damage.

On some airframes it is better to anti-ice the wing leading edges aswell, especially if using a weeping wing design like on many light aircraft.

As for this question, the answers beginning with "prevents" are correct (anti-icing rather than de-icing), and the ice does not form on the trailing edge of a wing (it can flow over the trailing edge in extreme cases but does not "form" there), so therefore the correct answer has to be that it "prevents the formation of ice on engine inlets."