Explanation

Long and difficult one. The best way to attack it is to figure out the second part and then pick the first blank accordingly.

In general, Moore was in a certain way: calm. So for the second and third blank F and H are the best. As it turns out, for the first one he was uncomfortable, then A is the best choice.
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I don't really get how we determine the shift that he was uncomfortable for (i)?

Moore was (i) _______ ill-at-ease.

ill-at-ease= uncorfortable

His (ii) _______ had always been a distinguishing feature. It was what made him a good con artist and a good informant. He was one of those men who accepted dares with an easygoing smile and did outrageous things with (iii) ______ that made him successful in the dangerous world in which he operated. But just now he was NOT FEELING very sure of himself.

Turns our he was weirdly uncomfortable

Regards
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thanks!

If he accpeted challenges with an easy smile and now he was not feeling sure, so the first blank will be uncharacteristically. THe other two blanks describe how he had always been prior too his indecision now, so both will be positive and support that he easily did dangerous tasks. so F and H

"Moore was (i) _______ ill-at-ease. His (ii) _______ had always been a distinguishing feature. It was what made him a good con artist and a good informant. He was one of those men who accepted dares with an easygoing smile and did outrageous things with (iii) ______ that made him successful in the dangerous world in which he operated. But just now he was not feeling very sure of himself."

Meaning- Moore was not typically ill at ease. His confidence had always been a distinguishing feature. With an easygoing smile he did outrageous things with courage but now he wasn't sure of himself.

A- Uncharacteristically means not typically. Works well.
B- Predictably means as expected. Opposite of what we want.
C- Naturally is irrelevant here.
D- Disquietude means state of anxiety. Illogical. That's the state he's in right now.
E- Magnanimity means generosity. Also illogical.
F- Aplomb means poise or self confidence. Works.
G- Obvious clumsiness is the opposite to what we are characterising this person as.
H- Sophisticated fearlessness works well with the general outlook of this character.
I- Wary watchfulness is illogical.

Who not C for the first blank ? Dosent naturally uncomfortable also work well herE?