Whereas the art critic Vasari saw the painting entitled the Mona Lisa as an original and wonderful (1) ___ feat, the reproduction of a natural object, the aesthetes saw it as (2) ____ that required deciphering.
Here, I’ve identified that blank 1 is a support to the apposition to the right (“reproduction of a natural object”). In his video (towards the end of Improve Your Skills Verbal - Determining Support/Contrast Text Completion Questions 1 - GregMat) he says it must be “difficult”, since “the reproduction of a natural object” is difficult to do. I feel like this is creating a story, and neither of the words “difficult” or “easy” are in the sentence (while I strictly try to maintain a context of using only those facts which are in the sentence, as Greg suggests).
You are correct in identifying the relationship between the blank and “the reproduction of a natural object.” You should consider the words before and after the blank as clues.
“Wonderful” before and “feat” after suggest that this is both a great and difficult thing. The phrase “the reproduction of…”—by the structure of the sentence—is the thing being praised as a wonderful and ___ feat.
Semantically, we’re looking for a word that represents the “greatness and difficulty of the act of reproducing a natural object.”
Your guess could be many things at this point (e.g., “impressive,” “difficult,” “great”). It could also be more nuanced, such as “technical” or “creative.”
As you can see, there’s a wide range of possibilities here.
So, you then have to consider the contextual clues you have as you explore the options to confirm the best answer