Correct option is A
The correct antonym of the given word is (a) Expensive.
Cheap: costing very little.
Synonyms: inexpensive, economical, low-cost.
Antonyms:
expensive, costly, overpriced.
Meanings of all options:
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Expensive: costing a lot of money.
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Ignorant: lacking knowledge or awareness.
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Old: having lived for a long time.
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Untangle: to make something less complicated.