In a nuclear fusion reaction, atoms: Question 5 options:

Explode

Split apart

Combine to form heavier elements

Cool down

Combine to form heavier elements

Explanation:

as opposed to fission which splits heavier atoms into lighter elements.

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