Sometimes It Is Impossible to "Inform" the Participant Fully at the Beginning

Multiple Choice

Sometimes it is impossible to "inform" the participant fully at the beginning of an experiment because

A) participants really don't want information
B) disclosing all information about the experiment might influence participants' behavior and invalidate the experiment.
C) participants cannot always guarantee their ability to come to all sessions of an experiment.
D) the research design being used is too sophisticated for participants to understand.