is not a unit of pressure. * A) armstrong
B) atmosphere
C) millimeter of mercury
D) Pascal

A) Armstrong is not a unit of pressure. In fact, I don't think it's even a unit at all, an "Amstrong" is a unit of length, if that's what you meant.

Atmospheres, Millimeters of mercury, and Pascals are all units of pressure.

Let me know if this helps!

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