It is well known that many species adapt to their environment

I think the answer should be D
B is not a conclusion- it is a fact which is clearly stated in the beginning of the sentence: "It is well known that many species adapt to their environment"
A, C E all relate to the plankton- sulphate-cloud example. This is used in the agument only as an example which is cited to support thw conclusion- an example cant be a conclusion in itself.

The only conclusion which is generic and not particular to example in the sentence is D

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.

The argument is posted at https://gmatclub.com/[/color]forum/it-is-well-known-that-many-species-adapt-to-their-112004.html but answer choices are phrased differently, order is different and OA is not provided.

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 environmentt 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 sulphate. These particles cause water vapor to condense,thus forming clouds. Indeed, the formation of clouds over the ocean largely depends on the presense 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.

What is the main conclusion of the above statements?

a.Plakton cause the surface of the earth to be cooler.
b.It is well known that many species adapt to their environment
c.The formation of clouds depends on the presense of sulphate particles in the atmosphere.
d.The characteristic of species altering their environmentt in ways that aid their own survival actually quite common
e.Certain planktons aid in the formation of clouds