Practice question

Pick B: Renin. Thinking about Excretory System in a practical way — what the structure does, or what the process achieves — leads you here. Clinically and academically, the same logic shows up again and again: the functional job described in the stem is exactly what Renin does in Excretory System. Hence Renin is correct. Treat this as a building block for the rest of Excretory System; neighbouring topics often reuse the same principle. Keep a one-line summary card for this idea and revisit it before the paper; short, repeated review beats long cramming sessions. If the wording feels dense, translate it into everyday language first, then map that plain sentence back onto Renin.