21 As a part of training, suitable audio-visual materials should be presented for the trainee instructors to review. The main purpose of screening such videos-films shall be to

A. spent a part of the class time to avoid fatigue and concentration losses.
B. make the trainees answer a set of suitable questions after viewing the material.
C. make the teaching process easier with minimum effort and time
D. divert attention of the trainees from the subject, if found lengthy.