change states MC

1.When a solid is melting, which of the
following statements is/are correct?


(1) The average potential energy of the
particles remains unchanged.

(2) The average separation between the
particles is increased.

(3) The average kinetic energy of the
particles remains unchanged.

A (1) only.
B (2) only.
C (2) and (3) only.
D (1), (2) and (3).

ans: c

我以為是 b
為何 3也正確?粒子間的空間不是增加了during melting嗎?
粒子在liquid 不應 move ramdomly ...ke 應有改變呀??