Thanks for the post, hyewonkim89! As a strategic point, just remember that a correct answer you get by eliminating all the wrong ones is worth just as many points as any other correct answer!
And you are completely correct that 1) for this
inference question we need some specific textual support and 2) the quote from line 15, "all partake of standard generic elements" is not enough to really support (C) as an answer. After all, corridos share a number of thematic conventions.
Lines 46-47, however, give us something far more specific. The despedida is a common element, and in particular, "[t]he first and third lines are a set convention". So all corridos share these lines! This completely supports
(C).
The Corridon'ts (A) The only mention of social gatherings is at line 16, and it has nothing to do with
Gregario Cortez.
(B) We know that
Kiansis is the earliest complete form surviving, but we have no information about whether 'most' are incomplete.
(D) Almost! They would have the same first and third lines of the despidida. But lines 47-8 point out that the second and fourth lines are variable.
(E) Kiansis is about cattle drives to Kansas, but that doesn't mean it was composed by someone not from the Border region.
Please let me know if this completely answers your question!