Which of the following electrocardiographic changes occur during second and third degrees of atrio-ventricular heart block?
(A) In second degree atrio-ventricular heart block, ECG shows presence of 'P' wave but complete absence of 'QRS & T' wave in the block beat
(B) In second degree atrio-ventricular heart block, ECG shows complete absence of 'P, QRS & T' complex for one beat
(C) In third degree atrio-ventricular heart block, ECG shows slow and independent ventricular rate characterized by 'QRS' complex that are dissociated from faster 'P' wave
(D) In third degree atrio-ventricular heart block, ECG shows variations in 'P-P' interval with or without 'P-R' interval
Choose the correct answer from the options given below: