If a substance is heated and then cooled off but remains as the original substance a change has occurred.
a) physical
b) chemical
c) structural
d) physical and chemical

I'm not a physicist, or an expert, but physical and structural both have a similar meaning, they both relate to appearances, but the question says "but remains as the original substance" so, if it isn't a visible change, then the only good answer left is a chemical change, hope this helps