I haven’t seen anyone awnser this question here before so thought I’d ask to help future users as well as to make sure I choose the right choice. The first image is gonna be a image of the actual question, Then the next image that is uploaded on here will be of the evidence I found in a lesson I did that I believe is what will help me to actually find the correct answer. But if I Am wrong feel free to correct me just make sure you explain why you think so. Appreciate it.

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