Explanation please

The OE usually comes up after some days I post the question.

However, in this case the boxers say that they need to bring up their wild or barbaric side to fight on the ring because usually, a civilized person does not do that: giving punches is never a solution.

B and F are the two words that fit

Let me know if this is still not clear

regards
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OE

barbaric, primitive Boxers are described as having to “punch each other in the face,” which isn’t “civilized.” In order to do this, they would need to access a part of themselves that was not so civilized (which would work well enough as a fill-in here). Seething and irate are an incorrect pair, both meaning “angry.” Insidious (seductive but harmful; treacherous, deceitful) and dynamic (characterized by constant change) have no relationship.
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Primitive doesn't necessarily mean barbaric. It is more inclined to how human live their life in archaic time. Saying primitive is barbaric is like saying ascetic is boring.