In 1963, Vladimir Nabokov finished his translation of Eugene Onegin

Explanation (from the source - Ready4GMAT):

There’s a lot happening in this sentence, so rather than attempting to identify the best way to phrase it ourselves, the best approach is to look at the differences between our answer choices and then identify the best version.

The first obvious difference is between (A), (B), and (C)’s beginning, “his translation,” and (D) and (E)’s beginning, “translating.” Though “Nabakov finished translating” is technically fine, it doesn’t make sense chronologically with the past tense “declare.”

Now that we’ve eliminated (D) and (E), the next major difference is how (A), (B), and (C) deal with “a text that.” By setting aside “requiring an excruciating process” in commas, (A) grammatically tells us that that information is not necessary to the sentence—but it is. Choice (B) uses “that” to organize the two pieces of information about the translation of Eugene Onegin and grammatically connects them with “and.” Though the sentence is still complex, it makes sense this way. Choice (C) does the same, but the verbs “had required” and “declared” don’t match like they should, and they do in (B), since both actions take place in the past.

The correct answer is Choice (B).