A Data Collection Protocol Calls for a Questionnaire to Be

A data collection protocol calls for a questionnaire to be administered to patients having knee replacement surgery after the third physical therapy appointment.Errors can be introduced into the study by

A) giving the questionnaire to all participants.
B) reading the questionnaire to the participants with poor reading skills.
C) giving the questionnaire to all participants when they arrive for their appointment.
D) giving the questionnaire to the participants after the appointment to be completed while they have a snack.