A 22-year-old female comes to the sexually transmitted disease (STD) clinic for her first visit. She tells the nurse practitioner that she has had four different sexual partners in the last six months and only one of them used a condom. She also admits that she used IV drugs on several occasions two years ago. She notes fever, weight loss, lack of appetite, and periodic difficulty breathing over the past few months. She has an HIV test performed, which is positive. The physician decides to do a confirmatory test for HIV. Which one of the following tests would the physician order? A. ELISA (Enzyme-linked immunosorbent assay) B. FACS (Fluorescence activated cell sorting) C. RAST (Radioallergosorbent Test) D. RID (Radial immunodiffusion) E. Western blot