Concept:An antonym is a word with the opposite meaning. "Dubious" means feeling doubt, uncertainty, or suspicion.
Explanation:- "Dubious" describes someone who is not sure or who doubts something.
- Its opposite is "certain", which means being completely sure and confident.
- The other choices — "unconvinced", "doubtful", and "hesitant" — all share the same idea of uncertainty, so they are not antonyms.
- Thus, the only word that directly opposes "dubious" is "certain".
Answer:Option D: certain