I think it would be B, please let me know if that's wrong!
I think it 700 million years because I took the same question and that’s what I put.
The correct answer is ( B )
C. Gradual
Hope this helps!
A marine layer is an air mass which develops over the surface of a large body of water such as the ocean or large lake in the presence of a temperature inversion. ... As it cools, the surface air becomes denser than the warmer air above it, and thus becomes trapped below it.
