A Researcher States in an Article, "The Subjects Acted as Their

A researcher states in an article, "The subjects acted as their own controls." If this is true, what does this imply?

A) Statistical significance was most likely calculated for each subject individually.
B) There were so few subjects that a separate control group could not be obtained.
C) Measurement of the subjects was made at least twice.
D) Two studies were performed.
E) The methodology was quasi-experimental.
F) The study was interventional.