The most abundant type of $WBC$ are

You are required to draw blood from a patient and to keep it in a test tube for the analysis of blood corpuscles and plasma. You are provided with the following four types of test tubes. Which of them will you $NOT$ use for this purpose?

The shape of the nucleus of $WBC$ is usually

Erythroblastosis fetalis (hemolytic disease of the newborn) is observed in marriages between:

$A$ person with an unknown blood group ($ABO$ system) has lost a large amount of blood in an accident and needs an immediate blood transfusion. $A$ friend of the person has a valid certificate of their own blood group and is ready to donate blood without delay. What could be the blood group of the donor friend?

The disease Erythroblastosis foetalis in the human embryo is caused due to: