How Was Level of Obedience Measured in Milgram's Research

How was level of obedience measured in Milgram's research?

A) The way in which participants played out their role ("prisoner" or "guard") .
B) The extent to which participants continued to be willing to administer electric shocks to the learner.
C) The extent to which participants asked the experimenter questions about how to proceed.
D) Whether or not participants were assigned to be the "learner" or the "teacher."