12. A fan blows the air and gives it kinetic energy. An hour after the fan has been turned off, what has happened to the kinetic energy of the air?
(A) it disappears
(B) it turns into potential energy
(C) it turns into thermal energy
(D) it turns into sound energy
(A) it disappears
(B) it turns into potential energy
(C) it turns into thermal energy
(D) it turns into sound energy