A 14-year-old girl develops a rash, abdominal pain, and arthralgias. She is also experiencing some nausea, vomiting, and crampy abdominal pain. On examination, she has a palpable purpuric rash on her buttocks and lower legs, a tender abdomen, and no active joint inflammation. Her stools test positive for blood, and urinalysis reveals RBCs and RBC casts. Her renal function deteriorates rapidly over several days. A renal biopsy is performed.For the above patient with GN, select the most likely diagnosis on renal biopsy.