Answer:
D. Acrid
Step-by-step explanation:
A. Sharp would imply some kind of pain usually, like "I have a sharp pain in my back"
B. Unpleasant could suggest some sort of bitter taste but it could also be used to describe other unpleasant or upsetting things.
C. Sour could be the correct answer but it most likely is not because Acrid describes a bitter taste better. Some people like sour things and do not see them as bitter like others might.
D. Acrid is an irritatingly strong and unpleasant taste or smell so this could relate to sour.