Can we do double possibility here, for exampled no study abandoned (implying fully exhausted) that it becomes mundane to ecologists
Yes, consider the below sentence as a possibility.
There are, as yet, no vegetation type or ecosystems whose study has been neglected to the extent that they no longer be inessential to ecologists.
There are, as yet, no vegetation type or ecosystems whose study has been completed to the extent that they no longer need ecologists.
Your guess on the double possibility, is actually analogous to the correct answer B, as far as I remember solving this question. However, in my opinion, “abandoned” does not fit perfectly. “Exhausted” is a better fit.