A 10-year-old patient is suspected of having acute glomerulonephritis. The test that indicates recent streptococcal infection is:

Rationale: A. A throat culture identifies current streptococcal infection but does not confirm a recent infection that may have triggered glomerulonephritis. B. An antistreptolysin O (ASO) titer measures antibodies produced in response to a recent group A Streptococcus infection, making it the most reliable test for linking acute glomerulonephritis to a prior streptococcal infection. C. Erythrocyte sedimentation rate (ESR) is a nonspecific marker of inflammation and cannot confirm recent streptococcal infection. D. Blood urea nitrogen (BUN), creatinine, and glomerular filtration rate (GFR) assess kidney function but do not indicate the causative pathogen.