Tony definitely disagrees with the claim that "human lives are best understood as series of completely disjointed vignettes," given his comment that we "depict human lives accurately by portraying characters whose personalities gradually develop through life experience." Gradual development through experience is certainly not "completely disjointed vignettes."

Raoul, on the other hand, definitely agrees with the claim that "human lives are best understood as series of completely disjointed vignettes," since, you know, he explicitly says, "Life consists... of a series of completely disjointed vignettes."

Since the two parties are committed to opposing views on this statement, answer A is correct.

Other answers:

B say that "novels and short stories employ the same strategies to depict human lives." Tony definitely disagrees. Raoul's position is a bit murky, so perhaps he does not really address this at all. But if we read into the statement that "the short story depicts human lives more faithfully than does the novel" then, if anything, Raoul is on the same side as Tony; he similarly disagrees with the claim that "novels and short stories employ the same strategies to depict human lives." So B is not a point at issue: The two parties agree with one another.

C says that "novels usually depict gradual changes in characters' personalities." Tony definitely agrees. Raoul doesn't actually really speak to this at all. If anything, we might imagine that he most likely agrees with this statement as well. Either way, it's not a point at issue.

D says that "only short stories are used as novelists' sketch pads." Tony technically doesn't address this. He does say, "A short story is little more than a novelist's sketch pad," but he doesn't say that only short stories are used in this way. Raoul, for his part, says nothing at all about this. So it's not a point at issue.

E says that "short stories provide glimpses of facts of character that are usually kept hidden." Nobody says anything about this (especially the "usually kept hidden" bit). It's not a point at issue.

A is the only winning option here.