Correct option is B
The correct antonym of the given word is (b) energetic.
Languid: lacking in vigor or vitality; slack or slow.
Synonyms: listless, lethargic, lazy.
Antonyms:
energetic, active, vigorous.
Meanings of all options:
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Lethargic: sluggish and apathetic.
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Energetic: showing or involving great activity or vitality.
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Sluggish: slow-moving or inactive.
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Indolent: wanting to avoid activity or exertion; lazy.