This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
T-cell are identified by - 
Select and explain. 
A. Rosette formation with sheep RBC, B. Immunoglobulins on their surface, C. EAC Rosette with sheep erytnrocytes, D. Have filamentous projections on their surface
A: Rosette formation with sheep RBC
Answer: A: Rosette formation with sheep RBC 
Explanation: Erythrocyte rosetting or E-rosetting is a phenomenon seen through a microscope where red blood cells (erythrocytes) are arranged around a central cell to form a cluster that looks like a flower. The red blood cells surrounding the cell form the petal, while the central cell forms the stigma of the flower shape. This formation occurs due to an immunological reaction between an epitope on the central cells surface and a receptor or antibody on a red blood cell. The presence of E-rosetting can be used as a test for T cells although more modern tests such as immunohistochemistry are available. May be caused by Plasmodium in malaria. Reff: www.mayoclinic.com