Who Among the Following Is Likely to Experience the Most

Who among the following is likely to experience the most serious case of post-traumatic stress disorder?

A) Peter, who was beaten by jailmates while he was being held for a minor violation
B) Dave, who witnessed a man being murdered on the street
C) Derrick, who was held hostage by a thief a grocery store
D) Pedro, who witnessed his family being tortured and killed by a military death squad