Oxygen is a byproduct of photosynthesis and, correspondingly, carbon dioxide the byproduct of respiration.
Oxygen gives our cells the ability to break down food in order to get the energy we need to survive. Although other animals may use different organs to breathe with, they all get oxygen into their bodies through respiration.
I don't know the options but my best guess would be erosion. Every time water comes on the beach is takes sand which erodes the beach. Hope that helps!
