The best transition between the four options presented to represent a time when water molecules are moving closer together would be A. Frost forms on a window pane.
The closest distance that the water molecules can do is when the water is in the state of being solid. It is known that the solid state of matter has the closest distance from molecule to molecule that when a molecule tries to move, the others move as well creating a vibration and thus producing heat in the process. When they are in a liquid state, they are quite far from each other. In a gas state, they really are far from each. This explains the difference in their characteristics.