Evening weather forecast

A, cloud is water vapor, gaseous water, rain is liquid water, and fog is formed by liquefaction of water vapor, which belongs to liquid state, so cloud, rain and fog are only two states of water, so they are wrong;

B, the three-state change of water is the interval change between molecules, and the molecular size is unchanged, so it is wrong;

C, the essence of cloud, rain and fog changes is that the interval of water molecules is changed and correct;

D, the lower the temperature, the slower the movement speed of water molecules, the smaller the interval, correct;

So choose ab.