Good question.
We can support the idea that its "ongoing" because all the verbs that relate to the critics or the general discussion are in the present tense.
The 1st sentence says that the Greek dramas "engender" considerable debate (not "engendered").
Snell argues / Barbu sugggests / Rivier thinks Snell's emphasis misrepresents / Lesky disputes both views
These are all present tense, so we can infer that this is a present debate (and, really, in the Humanities, where questions are rarely definitively settled, you can expect that every text has an ongoing debate about how to interpret it).
===other answers===
A) the author never takes a position or expresses an opinion. The three main critical viewpoints are simply presented.
B) establishing a "variety of themes" is too vague ... this passage was a series of perspectives on one specific theme, "individualism vs. divine intervention".
D) the author never takes a position or expresses an opinion, so we can't support "point out relative merits"
E) tempting wording. the passage is presenting the debate over human motivation's role in Greek tragedy. however, this answer is saying that the author wanted to show how Greek tragedy could be relevant to a separate debate. Greek tragedy IS the debate.
Good luck.