If you know what Dr. Jekyll and Mr. Hyde is about, then the answer is quite simple - the correct option is D. psychopathology.
Psychopathology is the study of mental disorders. Psycho means soul, pathos means suffering, and logos means study, so it is literally the study of why your soul suffers. Dr. Jekyll has a certain mental disorder which enables his evil counterpart/other personality, Mr. Hyde to come out, similarly to Bruce Banner and Hulk.