Read the following statements and select the correct option stating which one is true (T) and which one is false (F).
A. ABO grouping is based on the presence or absence of two surface antigens on leucocytes.
B. During first pregnancy there is least chance of occurrence of erythroblastosis fetalis due to Rh incompatibility
C. During blood clotting, conversion of fibrinogen to fibrin occurs by action of enzyme thrombokinase
D. All chordates possess chambered, muscular dorsal heart to pump blood throughout the body