Which of the following does not participate in the process of blood clotting?

The blood of $AB$ group donor can be transfused to a person with the blood group

Select the incorrect statements with reference to $Rh$ grouping.
$A$. Erythroblastosis foetalis is a condition observed having foetus with $Rh^{+ve}$ blood and mother with $Rh^{+ve}$ blood.
$B$. $Rh$ antigen is observed on $RBCs$ in the majority of human beings.
$C$. Before blood transfusion, $Rh$ group should also be matched.
$D$. $Rh$ incompatibility is observed when a pregnant mother is $Rh^{-ve}$ and the foetus is $Rh^{+ve}$.
$E$. Erythroblastosis foetalis can be avoided by administering anti-$Rh$ antibodies to the mother immediately after the delivery of the second child.
Choose the answer from the options given below:

What is the function of serotonin in the blood?

In a medicolegal case of accidental interchange between two babies in a hospital,the baby of blood group $A$ could not be rightly given to a couple with:

Mature human $RBCs$ are enucleated. Which of the following is the most appropriate explanation for this?
$(i)$ They do not need to reproduce.
$(ii)$ They are somatic cells.
$(iii)$ They do not perform metabolism.
$(iv)$ Their internal space is available for $O_2$ transport.