The correct answer is A. When the subject of a sentence is singular, add "_s" to the base form.
An easy example is "to exist", the base form is "exist" and A strawberry exists shows that you add s when a singular subject is used.
Answer:
I do not think you got anything wrong...Maybe the teachers thought you did?
Explanation:
Try to confront them saying something like...Are you sure I got this wrong, make sure YOU know you got something wrong, before confronting them, if you are sure everything is correct, you may confront.