Use an example to describe how the combulsity of a substance can be both useful and dangerous.

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.

specific gravity is the density of a substance divided by the density of water. since (at standard temperature and pressure) water has a density of 1 gram/cm3, and since all of the units cancel, specific gravity is usually very close to the same value as density

so "c" is the answer

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