The true answer is C.
The boat is attracted to the magnet by the force of magnetism.
Let me explain. If Ashley made the paper boat and place it on the water, gravity will try to pull the boat down, however no magnets are used in this situation.
Now if magnets are used in this situation and the paper clip is attach to the boat, rather than gravity pulling it down, the magnet will be pulling paper clip, causing the boat to move, so instead of gravity, it's magnetism.
Note: Magnets=Magnetism