I'm having trouble eliminating C.
- A certain process refers to non-highly evolved species altering their environment.
- Certain cases refers to plankton.
- Conditions under which a certain process can occur refers to the level of evolved-ness needed for a species to alter its environment.
- The generalization is that not only high-evolved species can alter their environment.
Therefore, answer choice (D) says: The generalization that not only evolved species can alter their environment is advanced on the basis of an examination of a case that did occur where plankton altered their environment.
Seems like it all fits to me. Maybe the problem is level of evolved-ness is not a condition. For it to be a condition, you'd have to show that a dialogue like below is compatible with the stimulus:
P: "We have a species and we want to see if it can alter its environment."
Q: "Is it either highly evolved or non-highly evolved?"
Q: "Then it meets at least one of the requirements for being able to alter its environment."
The stimulus isn't about determining conditions that species need to be able to alter their environment but rather finding out whether or not a general principle is correct.