The right answer is option B.Meaning:
Among the lithany of threats that many Israelis face, the potential for a nuclear-armed Iran is perhaps the most scary as this scenario could engulf the region in a violent war.
The keyword to note in the non-underlined portion of the sentence is
among. Among modifies three or more entities. Hence in the context of the sentence, Israel faces at least three more threats, out of which the threat from Iran's nuclear program is perhaps the most scary. More scary will not work since we have more than two threats. A can, therefore, be eliminated.
In C, possibly, perhaps is redundant since possibly and perhaps express the same idea of probability. We can eliminate C for wordiness.
In D and E, greatest and great are not appropriate because we are dealing with countable nouns. Threats are countable and they are modified rightly with among. We can eliminate D and E and be left with B as the best answer.
Among the litany of threats that many Israelis face, the potential for a nuclear-armed Iran is
perhaps the more scary as this scenario could engulf the region in a violent war. This would likely result in historically unseen amounts of destruction, even for a region whose history is marred by perennial violence.
A)
perhaps the moreB)
perhaps the mostC)
possibly, perhaps the mostD) possibly the
greatestE) possibly the
great