Answer: (D) all of the above.
Explanation:
The kidneys remove wastes and extra water from the blood to form urine. Urine flows from the kidneys to the bladder through the ureters.
Ammonia is an extremely toxic base and its accumulation in the body would quickly be fatal. The liver contains a system of carrier molecules and enzymes which quickly converts the ammonia (and carbon dioxide) into urea (waste).
Calcium excretion in the urine is a function of the balance between the calcium load filtered by the kidneys and the efficiency of reabsorption from the renal tubules.