Concept:The word 'prudent' means careful and wise about the future. Its opposite will mean lacking care or thought.Explanation:'Prudent' implies showing caution and foresight. 'Thoughtless' means doing things without thinking or caring. These are direct opposites.The other options are not antonyms: 'Cautious' and 'Sensible' are similar to prudent; 'Undicious' is not a standard English word.Answer:B. Thoughtless