Her coming to this place tomorrow is definite.

Answer: Option A

Definite : clearly stated or decided; not vague or doubtful.
Doubtful : feeling uncertain about something.
Regrettable : (of conduct or an event) giving rise to regret; undesirable; unwelcome.
Questionable : doubtful as regards truth or validity.
Unpredictable : not able to be predicted; changeable.

Antonym of Definite is Doubtful