Which sentence best fits at the marked point? "Coral reefs support around a quarter of all marine species. ▮ This makes their decline a concern far beyond the reefs themselves."
The sentence after the gap says the decline matters "far beyond the reefs". Option C strengthens exactly that link. The others are true but do not connect the two sentences.
Q4Vocabulary
In "the results were ambiguous", ambiguous means:
Ambiguous means it can be read in more than one way. Do not confuse it with ambivalent, which describes mixed feelings rather than unclear meaning.