Which of the following statements is true?
a. static characters are always the bad guys.
b. dynamic characters change mostly because of character vs. character conflict.
c. static characters often change due to internal conflict.
d. dynamic characters often change due to both internal and external conflict.

I believe D is the correct answer. "Static characters" aren't necessarily bad guys, they can be either good or bad. And C is incorrect because they don't change, they stay the same throughout the story. B is incorrect because that is not the reason why dynamic characters change mostly. So D must be the correct answer, both internal and external conflict can be the cause of their change.

Slavery was the key of sugar