OE


nonchalance, indifference In this sentence, the key is the word “belied,” which functions as a kind of reversal signal. Belie means “to misrepresent or contradict,” suggesting a contrast to “his deep sense of responsibility.” A good fill-in for the blank would be not caring. Mirth and felicity are an incorrect pair, both meaning something like “happiness,” though mirth additionally often implies laughter. Concern and sagacity (keen judgment) have no relationship.
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