A 21-year-old college student presents with fatigue and dark urine one week after recovering from atypical pneumonia. He reports Raynaud phenomenon with painful, pale fingers in cold weather. Vital signs show HR 102/min, BP 118/76 mmHg, RR 16/min, temp 37.2°C. Laboratory studies reveal hemolytic anemia with elevated indirect bilirubin and positive cold agglutinin test. Peripheral blood smear shows no schistocytes. Which of the following is the most likely cause of this patient's condition?

1. A)Mechanical trauma to erythrocytes from a prosthetic valve
2. B)IgG antibodies directed against Rh antigens
3. C)Loss of intrinsic factor with megaloblastic change
4. D)IgM antibodies against red cell I antigen after Mycoplasma infectionGABARITO
5. E)Deficiency of spectrin in the red cell membrane