Answer:
Nonmetal + Nonmetal —> covalent compound (usually)
Explanation:
Covalent compounds are formed when two nonmetals react with each other.
Benthos are "organisms inhabiting the seafloor" according to one source, so I would say the answer is C.
When atoms bond together to form molecules, they share or give electrons. If the electrons are shared equally by the atoms, then there is no resulting charge and the molecule is nonpolar.