A Blood Sample from a 90-Year-Old Man Was Submitted to the Blood

A blood sample from a 90-year-old man was submitted to the blood bank for a type and screen before surgery.The forward type demonstrates as a group A,whereas the reverse type appears to be group AB.The most likely cause of the discrepancy is:

A) contaminated reagent antisera.
B) rouleaux formation.
C) that the patient has autoantibodies.
D) that patient has low-titer isoagglutinins.