A shoreline
Shores can be found as the area that separates the stretch of land from a body of water.
A beach doesn’t change on a daily basis (without humans)
A coast is the land near the sea so, it doesn’t really change.
A shoreline though, is the line between land and sea/ocean. A shoreline is constantly getting corroded and changed on a daily basis, especially compared to the other answers.
So the answer is A, a shoreline.
I hope this helps!
