Marine snow is
a. pieces of organic matter that were once part of living organisms
b. a mixture of living plankton
c. snow from land that has entered aquatic ecosystems
d. large salt crystals that have not dissolved in ocean water

The right option is; a. pieces of organic matter that were once part of living organisms  

Marine snow are pieces of organic material that emanate from the upper layers of the ocean and falls to the seafloor. Marine snow is composed of various organic substances, such as dead organisms, and protists, fecal matter, sand, and other inorganic particles. Marine snow provides as a good source of energy for deep sea organisms.

b

explanation: