Answer:
The correct answer is A. Sunlight.
Explanation:
The ocean contains many plants and protists that can make their food, such as phytoplankton. These organisms are photoautotrophs, which means that they need light to photosynthesize, otherwise they would not be able to produce primary production.
Photosynthetic activity of marine organisms depends on luminous intensity, but solar light can only reach up to a certain depth in water, which is not much deeper than the surface. So every photoautotrophic organism must inhabit near the surface to get the necessary energy amount.
Each organism and species can live at different depth levels according to their needs, but all of them are restricted to the surface or near the surface because they need solar light.