Symptoms of ptsd include all of the following except
intrusive thoughts or memories of a traumatic event
avoidance of things that remind one of a traumatic event
jumpiness
physical complaints that cannot be explained medically

d. physical complaints that cannot be explained medically, is not a symptom of PTSD.

Explanation:

Posttraumatic stress disorder (PTSD) is a type of mental disorder which is caused by  exposure to a traumatic event. The traumatic event that can induce this disorder are traffic collisions, loss of loved one, sexual assault, natural disaster terrorism etc.

Some of the symptoms of the posttraumatic stress disorder include flashbacks of the traumatic event, recurring dreams, disturbing thoughts, irritability, avoiding things related to the event, detachment from others and jumpiness.    

Therefore, physical complaints that cannot be explained medically is not a symptom of PTSD.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.