chemical change: a change in the makeup of a substance. so:
a. if you melt cheese it is still just cheese, only melted
b. if you grind something into a powder it is still the original substance, only in a different form
c. if a firework explodes, the chemical makeup of the firework itself changes from the heat applied to make it shoot into the air and explode. it then turns to ash, so this would be the correct answer.
d. if you iron a shirt, it's still a shirt, only flattened
answer: C