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.

Static characters are not always bad guys. They simply are supportive roles as these characters don't change throughout the story. Dynamic characters undergo a change of heart as it were throughout the plot. This change can be caused from both internal and external conflict. An example of a dynamic character is a bad guy who realized his wrongs and changed into a good guy. 

The best answer is thus D.