The correct answer is A. diffident.
A diffident person is lacking in self-confidence or assurance. They may be hesitant to speak up or take risks, and they may worry about what others think of them.
A timid person is also lacking in self-confidence, but they may be more fearful or anxious than diffident people. They may avoid social situations or new experiences, and they may be easily intimidated.
A reserved person is quiet and restrained. They may not be as outgoing or talkative as other people, but they are not necessarily lacking in self-confidence.
A shy person is also quiet and restrained, but they may be more uncomfortable in social situations than reserved people.
They may blush easily, avoid eye contact, or speak in a soft voice.In conclusion, the antonym of confident is diffident. A diffident person is lacking in self-confidence or assurance, while a confident person is sure of themselves and their abilities.