In a standard $ECG$,what does the $QRS$ complex represent?

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

Describe in detail: $ECG$.

In all the leads of $ECG$,all following are positive waves except

Given below are two statements.
Statement $I$ - Graphical recording of electrical variations detected at the surface of body during their propagation through the wall of heart is electrocardiograph.
Statement $II$ - The instrument used for the graphical recording of electrical variations detected at the surface of body during their propagation through wall of heart is electrocardiogram.
In the light of above statements,select the correct option given below:

Match List $I$ with List $II$.

List $I$	List $II$
$A$. $P$-wave	$I$. Beginning of systole
$B$. $Q$-wave	$II$. Repolarisation of ventricles
$C$. $QRS$ complex	$III$. Depolarisation of atria
$D$. $T$-wave	$IV$. Depolarisation of ventricles

Choose the correct answer from the options given below: