Which of the following correctly describes the importance of demonstrations to a scientific investigation?
a. in a demonstration, empirical data is collected.
b. a demonstration is a process involving scientific investigation.
c. in a demonstration, the effect of one thing on another is measured.
d. a demonstration shows how something works, often including models.

what is the question?

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