You are answering a USMLE-style medical question. Question: An 11-year-old boy presents to your office with pitting edema and proteinuria exceeding 3.5g in 24 hours. You suspect that this patient has experienced a loss of polyanions in his glomerular basement membranes. Which of the following findings would confirm your diagnosis? Options: A) WBC casts in the urine B) Selective albuminuria C) Negatively birefringent crystals in the urine D) Bence-Jones proteinuria Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.