Option A: Right
This statement appears the best deductive analysed option in that , it does not seek to overemphasize or overestimate the action of these fungus on the trees. The use of ''can'' means it didn't state specifically that without it the trees won't survive which is the position of the writer. It also links the opening statement directly with the concluding statement without stress.

Option B: Wrong
This statement is very true. It derives nutrients from the fungi it eats because it won't survive if not. The use of the adverb ''entirely'' explains it all. Nevertheless, it doesn't explain on general terms the whole passage which does not qualify it to be the most correct option.

Option C: Wrong
This is too generalistic in nature for a statement merely drawing inference from a perspective. Trees must be capable of existing but the addition of this fungal activities only aids nutrients addition, development and ''assist'' in protection with emphasis on ''assist''.

Option D: Wrong
It is not specifically inferred what their viability would mean even if it were above the ground level because, it was stated in the passage that the red-backed vole feeds on the fungi that grows above the ground. It may not be entirely viable because it is needed for the green environment.

Option E: Wrong
This is a supposition and has little or no element of ideal when it comes to matter of the environment. It is also too generalistic.