Match the columns:

Column-$I$ (Blood group)	Column-$II$ (Antibody)
$A$. $A$	$P$. $b$
$B$. $B$	$Q$. $a$
$C$. $AB$	$R$. $nil$
$D$. $O$	$S$. $a$ and $b$

(A) The $ABO$ blood grouping system is based on the presence or absence of two surface antigens on the red blood cells ($A$ and $B$).
$1$. Individuals with blood group $A$ have antigen $A$ on their RBCs and antibody $b$ (anti-$B$) in their plasma.
$2$. Individuals with blood group $B$ have antigen $B$ on their RBCs and antibody $a$ (anti-$A$) in their plasma.
$3$. Individuals with blood group $AB$ have both antigens $A$ and $B$ on their RBCs and no antibodies $(nil)$ in their plasma.
$4$. Individuals with blood group $O$ have no antigens on their RBCs and both antibodies $a$ and $b$ (anti-$A$ and anti-$B$) in their plasma.
Therefore,the correct matching is: $A-P, B-Q, C-R, D-S$.