Answer:
B. Solid to Liquid
A.P.E.X.
Explanation:
I'm no expert at this but if you think about it, a fixed shape is a solid figure such as an ice cube and when that melts, the solid (Ice Cube) turns into a liquid (Water). A liquid most of the time has a fixed volume but can still change shape such as going into a droplet of water or going into a spiral down the drain.
(Lemme know if this makes sense please)
