Mammalian $RBCs$ are..... in shape.

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

Which blood group is the universal donor?

Given below are two statements:
Statement $I$:
The coagulum is formed of a network of threads called thrombins.
Statement $II$:
Spleen is the graveyard of erythrocytes.
In the light of the above statements,choose the most appropriate answer from the options given below:

Incompatibility between $\text{Rh}$-positive and $\text{Rh}$-negative blood during transfusion can lead to $:-$

Blood platelets are found in $.......$.