(A) In the languages of some of the cultures of Alondia, the word for “explosion” can refer to any kind of disaster.
This choice actually weakens the conclusion because if “explosion” may mean something other than explosion itself, then the author’s conclusion about the actual explosion is under doubt since those cultures may mean anything other than explosion.
(B) A small number of the stories also include an account of a large wave that followed the explosion.
Again weakens.
Small number of stories may mean 2 or 3 among thousands and thus adds nothing to the information already present.
Moreover, the conclusion is about explosion.
(C) Most volcanic eruptions are only audible to humans within a few hundred miles of the source.
This choice also weakens the argument by saying that the explosion may not have been heard by many cultures who are spread over a very large geographic area. So, many of them may have never actually know about the explosion but simply may have made up it.
(D) Because ancient cultures often associated natural events with specific deities, many stories in these cultures cite such events as a way of indirectly referencing those deities.
This choice almost has nothing to do with the conclusion. These people may have referenced those deities with actual or made up story about the explosion.
(E) Until relatively recently, most of the people of Alondia had had no contact with one another, either direct or indirect, for at least five thousand years.
Correct because this choice removes one weakener. If the reverse were true, and most of these people contacted each other, then probably they may have heard about the explosion from one another, from those actually made up the story. But E eliminated this weakener, and shows that probably those people actually saw that explosion because all of them could not make up such story independently - too much to be coincidence.
So E