Which two of the following statements best describe the methodological characteristics of Milgram's (1963) baseline study of obedience?

Select two options only.

A. It utilized a self-selected (volunteer) sampling method. B. It demonstrated high ecological validity due to the realistic setting. C. It manipulated an independent variable to establish a cause-and-effect relationship in the baseline trial. D. It gathered both quantitative and qualitative data. E. It employed a repeated measures design to compare participants' behaviour at different shock levels.