In choice <em>C</em>, the two magnets are closer together so it wouldn't have much attractive force. Whereas, in choice <em>D</em>, the two magnets are further apart so it might have the greatest attractive force.
If I were you, I would choose <em>D</em>, but I suck at school so it probably isn't <em>D</em>.
When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles determines the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space.
