This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Medicine
Which of the following blood system have Carbohydrate antigen 
Select and explain. 
A. Rh, B. Kell, C. Lewis, D. Duffy
C: Lewis
Answer: C: Lewis 
Explanation: Antibodies to &;Lewis system&; carbohydrate antigens are the most common cause of incompatibility during pretransfusion screening. The Lewis gene product is a fucosyltransferase and maps to chromosome 19. The antigen is not an integral membrane structure but is adsorbed to the RBC membrane from the plasma. Antibodies to Lewis antigens are usually IgM and cannot cross the placenta. Lewis antigens may be adsorbed onto tumour cells and may be targets of therapy.Reference: Harrison&;s Principles of Internal Medicine; 19th edition; Chapter 138e&; Transfusion Biology and Therapy