Counter-Argument: Greco's paintings are elongated which was unheard-of European paintings at the time. Thereby, Greco had an visual impairment which led to those distortions in his paintings.
Conclusion: The reasoning of impairment behind the elongations in his paintings is incorrect.
Question: What can be the premise to the author's conclusion?(A) several twentieth-century artists have consciously adopted from El Greco’s paintings the systematic elongation of the human formWe are talking about Greco's time (16th-17th century), what happened/inspired later 20th century artists is irrelevant. Also, it has no bearing on whether elongations in Greco's arts were due to impairment or not.
(B) some people do have elongated bodies somewhat like those depicted in El Greco’s portraitsSome people having elongated bodies does not give reason to conclude that impairment isn't the reason behind distortions in his paintings. It does give alternate reasoning to it, but does not help the fact that Greco's paintings were systematically elongated.
(C) if El Greco had an astigmatism, then, relative to how people looked to him, the elongated figures in his paintings would have appeared to him to be distortedThis gives good reason to argue against the reasoning that his impairment is behind the elongations in his paintings. Keep it for now.
(D) even if El Greco had an astigmatism, there would have been no correction for it available in the period in which he livedIf anything, it supports, rather than doubt, the idea that the visual impairment was behind the distortions in his paintings.
(E) there were non-European artists, even in El Greco’s time, who included in their works human figures that were intentionally distortedThis is quite tempting, and would have worked if non-European artists had not been explicitly stated. We know that intentional distortion of human figures was unprecedented in European painting. Characteristics of non-European artists is not relevant here.(C) is the best choice by process of elimination.