The correct answer is C. stubborn.
Adamant means “unwilling to change one’s opinion or course of action.” In the context of the question, the speaker tried to persuade the person to change their mind, but they refused to do so. This suggests that the person is stubborn.
The other options are incorrect because they do not accurately describe the person’s behavior. Foolish means “lacking good sense or judgment.” Aggressive means “ready or likely to attack or confront.” Defensive means “protecting oneself or one’s interests against attack or criticism.”
In the context of the question, the person’s behavior does not suggest that they are foolish, aggressive, or defensive. They are simply unwilling to change their mind.