一道GRE填空求大神解释

一道GRE填空求大神解释
If one could don magic spectacles – with lenses that make the murky depths of the
ocean become transparent – and look back several centuries to an age before
widespread abuse of the oceans began, even the most (i) ____ observer would
quickly discover that fish were formerly much more abundant. Likewise, many now-
depleted species of marine mammals would appear (ii) ____. But without such
special glasses, the differences between past and present oceans are indeed hard to
(iii) ____.







Blank (i)
(A) casual
(B) prescient
(C) clearheaded



Blank (ii)
(D) threatened
(E) plentiful
(F) unfamiliar



Blank (iii)
(G) ignore
(H) discern
(I) dismiss



不懂啊!最好有翻译……