Explanation

The blank structure for this problem is tricky; in such cases you need to pay attention to the specific words in the sentence that give hints to the meanings of the blanks.

For the first blank, you are looking for a modifier to “comprehension.” This “comprehension,” you learn, is impeded… by labyrinthine
complexities. In other words, total, or exhaustive, comprehension is difficult because of these complexities.

For the second blank, the key word is “reliable.” The relation of this word to the blank is given by “even the most,” telling you that these vintages are subject to something opposite to “reliable” — that is, remarkable variance.

An exhaustive, remarkable variance.
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confused with first blank still

exhaustive leads to labyrinthine complexities.

Question:

(i) __________ comprehension of the character of Italian wine is impeded not only by labyrinthine complexities of vineyards and varietals, but also by fluctuations in environmental conditions from year to year, which render even the most reliable vintages subject to (ii) ___________.


We know that some kind of comprehension was impeded by labyrinthine complexities of vineyards and varietals.

What kind of comprehension is impeded(prevented, obstructed, stalled) by labyrinthine complexities of vineyards and varietals, fluctuations in environmental conditions from year to year?

Given the list of challenges, we can say a complete or thorough comprehension is impeded or obstructed. Only an exhaustive fits the bill.

It cannot be a futile comprehension because, it means a failed comprehension, and such a failed comprehension does not need any of obstruction or impediment. Irredeemable is too judgmental and qualitative and is the wrong choice.

Now, we are told that these fluctuations in environmental conditions from year to year, render even the most reliable vintages subject to something. What can it be?

Now since even an exhaustive comprehension is not possible because of labyrinthine complexities and varieties, and now we even have fluctuations in environment, we can say even the reliable vintages become subject to variations and are no longer of just one type. So remarkable variance is the correct answer.

The adjectival phrase "even the most" before "reliable" makes us look for a word which suggests unpredictability or maximum unreliability , and only a remarkable variance can convey that sense.
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