What is the significance of the H antigen in the ABO blood group system?

A It is the precursor to the A and B antigens ✓
B It is responsible for the production of anti-A and anti-B antibodies
C It is a high-frequency antigen found on red blood cells
D It is an enzyme involved in the synthesis of ABO antigens

Explanation

The H antigen is the precursor to the A and B antigens in the ABO blood group system, and its presence or absence determines an individual's ABO blood type.

Source

Modern Blood Banking and Transfusion Practices
Hematology Hematology: Blood Grouping and Crossmatching Hematology: Blood Grouping and Crossmatching Medium MEDICAL Confidence: high