Answer:
C. Individuals collaborate to find a way to return the sea level to normal.
Explanation:
When the sea level returns to normal, humans will recover land and life may soon get back to normal too. This would certainly be an optimistic turn of events.
The mood (or tone) of the prologue is considered as sombre, dark, macabre... since from the start we're being told that this story is going to be a story of love, death and loss.