The correct answer is (c.) unicellular eukaryotes. Unicellular eukaryotes apply to most protists. Protists are grouping of eukaryotic cells that do not form any natural group. These eukaryotes include the Golgi apparatus and mitochondria, and for plants they include chloroplasts.
The answer is C because it is an example of evolution or adaption.
Earth would basically look like the Moon; minus the craters, of course. This is because with no atmosphere to hold all of the Oxygen near the surface, all life would die off fairly quickly.