In a standard ECG which one of the following alphabets is the correct representation of the respective activity of the human heart?

Question

$\begin{array}{1 1} \text{a. S-Start of the systole} \\ \text{b. T-End of diastole} \\ \text{c. P-Depolarisation of the atria} \\ \text{d. R-repolarization of the ventricles.} \end{array}$