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 foetalis due to Rh incompatibility.
( C ) During blood clotting, conversion of fibrinogen to fibrin occurs by action of enzyme thrombokinase.
( D ) All chordates prossess chambered, muscular, dorsal heart to pump blood throughout the body.