The first section ("While the parasitic.....preys on") in para-speak tries to say that there is some parasitic plant that feeds off of vegetation. The "while" alludes to a contrast later in the sentence. The rest of the sentence corroborates this contrasting idea, particularly with the "debilitating....in some ways" phrase later on.

Given the blank (i) and blank (ii) location, we're looking for two positive phrases. Something like "helps" for blank (i) and the contrast of "debilitating" for blank (ii). Looking at the choices for blank (i), only C <enhances> reflects this positive tone and fits the meaning. Next, the opposite of "debilitating" follows with D <beneficial> . E <singular> is not supported by the sentence - also sort of redundant. F <interconnected> might be tempting if you are drawn in by the "linking....tendrils" phrase. However, blank (ii) is far closer to the "debilitating" clue. Also, F <interconnected> doesn't promise the positive tone we're seeking here.