Cells are
a. characteristic of eukaryotic but not prokaryotic organisms
b. limited in size to 200 and 500 micrometers in diameter
c. only found in pairs, because single cells cannot exist independenty
d. characteristic of prokaryotic and eukaryotic organisms

The correct answer is D. Characteristic of prokaryotic and eukaryotic organisms

Explanation:

Cells are the basic unit of life as all living organisms are made of one or more cells; additionally, all cells are surrounded by a membrane and contain substances and organelles that allow them to grow, obtain nutrients, reproduce and other basic functions for life. Additionally, as cells are the basic unit of life they are characteristic of both prokaryotic and eukaryotic organisms, although the structure in cells differs in both as in prokaryotic organisms there is no defined nucleus or bounded organelles. Thus, cells are characteristic of prokaryotic and eukaryotic organisms.

there really is life in the deepest part