B, if P is glucose, it should be 0 when it reaches the ureter, and it should not become larger. This is an error term.
C, if Q is protein, the blood is filtered back to the blood when it flows through the glomerulus, and the liquid is 0 when it flows through the renal tubule, so it should not be changed. This is an error.
D and P are urea, and the concentration increases when they flow through ureter because most of the water is reabsorbed into the blood by renal tubules, and Q is glucose.
So the answer is: D.