TOW (& Answer)...

The question was in what two ways can marine plants be classified?  Marine plants can be classified as either plankton or benthos.  Plankton are plants that float freely on the water’s surface.  Benthic plants are rooted in the sea floor.

The question (& answer) were taken from p. 58 of volume 1 of The Encyclopedia of Biomes edited by Marlene Weigel.  The book was published in 2000 by UXL.