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 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. Plankton 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 presence of sulphate particles in the atmosphere.
d. The characteristic of species' altering their environment in ways that aid their own survival is actually quite common.
e. Certain planktons aid in the formation of clouds.