The correct answer is A. bitter.
A bitter odour is one that is unpleasant and often associated with something that is poisonous or harmful. It is a sharp, acrid smell that can be quite strong.
A repulsive odour is one that is extremely unpleasant and often associated with something that is dirty or decaying. It is a strong, foul smell that can be quite nauseating.
A strange odour is one that is unusual and unfamiliar. It is a smell that is not easily identified and can be quite unsettling.
An unpalatable odour is one that is not pleasant to smell. It is a smell that is not enjoyable to take in and can be quite off-putting.
In the context of the question, the room is filled with a delicious odour. This means that the odour is pleasant and enjoyable to smell. It is not bitter, repulsive, strange, or unpalatable.