Question

How can you tell that the fireworks exploding during a Fourth of July display do not all contain the same ingredients?

Answer 1

A- Different colours of explosions. Different materials will burn different colours.
Element & flame color
Calcium= orange-red
Strontium= red
Barium pale= green
Copper= blue-green (often with white flashes)

Answer 2

I am 90% sure it's A. I know that the different ingredients causes them to be different colors.  The shapes and timings are usually man made.