In the Regions of the Dead Zone in the Gulf

In the regions of the dead zone in the Gulf of Mexico just west of the Mississippi River delta,oxygen levels are

A) highest at the bottom of the ocean,where the algae do not get enough sunlight to survive.
B) highest at middle ocean depths,where plants produce the most oxygen.
C) highest at the ocean surface,away from oxygen depleting bacteria.
D) lowest at the ocean surface,where fertilizers bind to and remove the oxygen.