OFFICIAL EXPLANATION

This sentence is dense: it has many words typically tested on the GRE, such as testimony, blatant, masquerade, and poise. The sentence describes Tom and his previous nature of not being a master of pretense - one who pretends or fakes. Later on, he became a testimony (evidence, demonstration) to something and presented a blatant (obvious; clear) masquerade (pretense; disguise) of humility, with poise (composure, coolness).

If we work out from the known part of the sentence, we can infer that Tom presented humility with poise. You can assume poise to be calmness or balance that is required to present something. And why was there a need to present humility? That means it's not coming out naturally and he was fabricating/faking it. Thus, the blank has to take a word with a negative connotation, and should be a synonym to fabrication. So, a suggestive fill-in is fabrication.

The hint-phrase is even a blatant... something of humility was presented with poise and signal words - 'pretense' and 'poise' further help to understand the fill-in.

Let us pre-empt the fill-in; it should be negative and relatable words from the synonym family of fabrication.

Let us understand the meanings of the option words from the blank.
A. ingenuity - cleverness; skill
B. peevishness - irritability; fussiness
C. magnanimity - generosity; lavishness
D. affectation - artificiality; insincerity
E. enunciation - diction; articulation

The correct answer would be 'affectation'. While 'ingenuity' would have been a close call, it's more of a positive word and used in a general context. Though 'peevishness' is negative in the context, the meaning of irritability does not match the required context. The other words are not relevant in the context.

The correct answer is 'affectation'.