It is well known that many species adapt to their environment, but it is usually assumed that only the most highly evolved species alter their environment in ways that aid their own survival. However, this characteristic is actually quite common. Certain species of plankton, for example, generate a gas that is converted in the atmosphere into particles of sulfate. These particles cause water vapor to condense, thus forming clouds. Indeed, the formation of clouds over the ocean largely depends on the presence of these particles. More cloud cover means more sunlight is reflected, and so the Earth absorbs less heat. Thus plankton cause the surface of the Earth to be cooler and this benefits the plankton.

Of the following, which one most accurately expresses restated conclusion of the argument?

A. The Earth would be far warmer than it is now if certain species of plankton became extinct.
B. By altering their environment in ways that improve their chances of survival, certain species of plankton benefit the Earth as a whole.
C. Improving their own chances of survival by altering the environment is not limited to the most highly evolved species.
D. The extent of the cloud cover over the oceans is largely determined by the quantity of plankton in those oceans.
E. Species such as plankton alter the environment in ways that are less detrimental to the well-being of other species than are the alterations to the environment made by more highly evolved species.

My Ques: What is the OA? C or D?