Which blood group is the universal recipient?

The buffer salts present in the blood are

What physiological circumstances lead to erythroblastosis foetalis?

Mention the life span of Red blood cells. (in $days$)

Between persons of which two blood groups is the blood transfusion not possible?

Match the Column $I$ (blood corpuscles) and Column $II$ (stem cells/precursors from which they are formed).

Column $I$ (Blood corpuscles)	Column $II$ (Stem cells/precursors)
$i$. Thrombocytes	$a$. Lymphoid stem cells
$ii$. Granulocytes	$b$. Megakaryocytes
$iii$. Erythrocytes	$c$. Myeloid stem cells
$iv$. Agranulocytes	$d$. Reticulocytes

Choose the correct option given below.