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Leping wedding service caiqi
A

A, fireworks have new substances, which belong to chemical changes. Correct;

B, there is no new substance produced during the balloon lift-off, which is a physical change. Mistakes;

C, there is no new substance generated in the process of colorful flags flying, which belongs to physical changes and errors;

D, there is no new substance generated in the process of sound, which belongs to physical changes. Mistake.

So choose a.