Correct option is D
The correct answer is (d) thieves
The plural form of "thief" is "thieves". In English, some nouns ending in -f or -fe form their plurals by changing the -f or -fe to -ves.
Examples:
Thief → Thieves
Wolf → Wolves
Knife → Knives
Additional Information:
Synonyms of thief: Robber, Burglar, Pickpocket, Bandit, Looter, Intruder, Shoplifter, Mugger, Pilferer, Larcenist