The incident affected him so much that he could not forget it for several days.

The correct answer is: A. upset.

The word “upset” means to make someone feel unhappy or worried. In this case, the incident upset the person so much that he could not forget it for several days.

The other options are:

• B. changed: This word means to make something different. In this case, the incident did not change the person, but it did upset him.
• C. influenced: This word means to have an effect on someone or something. In this case, the incident did influence the person, but it did not control him.
• D. controlled: This word means to have power over someone or something. In this case, the incident did not control the person, but it did upset him.