Human urine is usually more acidic than most other body fluids ...

[j_sun]

Human urine is usually more acidic than most other body fluids because
A) hydrogen ions are actively moved into the filtrate.
B) the sodium transporter exchanges one hydrogen ion for each sodium ion.
C) excreted plasma proteins are nearly all acidic ions.
D) excreted amino acids are in abundance.
E) potassium and sodium exchange generates lots of acidity.

[sammy]

I remember it was A

[j_sun]

Thanks dude! Marking this solved.