This question asks for how a specific term has been used in the passage.
Looking at the progress of the passage and the part after ":", today's environmentalists embraces equilibrium model of ecology. What's interesting here is the author's intention for using "mystique." Hearing the word "mystique" gives you a sense of yearning. And this well-accounts for the "fervor" from the answer choice A), which also states, "adhere to the equilibrium theory."
Let's see other answer choices.
B) We are only given that past attitude regarding environmental crisis has gradually changed from 1970s (46), but not given exactly when today's environmentalists started supporting this. So, we have no idea if this model has "recently been supported" to start with. Also, we have no reference to "empirical scientific research."
C) Aside from "appreciation", it is the equilibrium model of ecology itself. And we have no clue to make us think that there is "appreciation" embedded in "mystique"
D) Equilibrium model of ecology has been understood and endorsed by nowadays environmentalists for all we know.
E) Tempting. I originally chose this and got this question wrong. Since the word "mystique" is so unfamiliar to me that it was closer to "widespread support", which is supported from the continuing portion of the text. But the problem with this answer choice is that "scientific community" is too wide and general. We have been talking about environmentalists and reformers, not scientists.