A 500 Hz sound wave and a 400 Hz sound wave travel through the air. Which of the following characteristics must be different for the two
waves?

hey , the answer is c

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me

im srry but ur wrong the answer is d a smooth rock, some red dirt, and an empty bird's nest.

a. carbon monoxide from car exhaust

b.particulate matter, such as soot

c.water vapor from a factory smokestack

d.acid rain

these are the answer choices im on that question right now