Plankton are most commonly found in the a. pelagic zone
b. littoral zone
c. benthic zone
d. all of the above

A  I'm doing it on edge now

Explanation:

Although most of these organisms are motile (moving), they cannot swim or move against currents, but they can move vertically in the water column. Many marine plankton are found in the deep waters of the outer ocean, or pelagic waters, whereas others are found in the shallow waters known as the neritic zone.

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