In an ECG, the depolarization of atria is indicated by
a)	P-wave	b)	Q-wave	c)	R-wave	d)	S-wave

(a)

ECG is the graphical recording of electrical changes that accompany the cardiac cycle. It is represented by five waves – P, Q, R, S and T. P-wave indicates depolarization, of atria, QRS complex indicates ventricular depolarization, while T-wave indicates ventricular repolarization.