Dr LaGuardia Is a Cognitive Neuroscientist Who Is Interested in the Effect

Dr. LaGuardia is a cognitive neuroscientist who is interested in the effect of brain concussions on the ability to recognize faces. He conducts a quasi-experimental study in which he examines football players before and after the regular season using the Benton Facial Recognition Test (a published, widely used measure of one's ability to recognize faces) to compare those who received concussions to those who did not. He finds that players who had concussions during the regular season performed worse on the Benton Facial Recognition Test than did players who did not experience concussions.
Which of the following is true regarding external validity in Dr. LaGuardia's study?

A) Because Dr. LaGuardia selected participants who actually experienced concussions, the study has strong external validity.
B) Because Dr. LaGuardia's study is a quasi-experiment, it is impossible to obtain external validity.
C) Because Dr. LaGuardia's dependent variable was assessed in the laboratory, the study has limited external validity.
D) Because Dr. LaGuardia selected a widely used measure, his study generalizes to other applications of this measure.