Which Statement Best Describes a Methological Problem with the Study

Which statement best describes a methological problem with the study of the Big Five conducted by Srivastava and colleagues (2003) ?

A) The responses were based on self-report rather than observed traits.
B) The use of Internet sites provides a representative sample.
C) They drew cause-and-effect conclusions based on correlational data.
D) You cannot generalize on the basis of case study data.