Proteins not ingested by humans are found in human cells. The presence of
these proteins is most directly a result
of

The correct answer is option A and B.

Explanation:

The kidneys play an essential role in sustaining a constant internal environment, that is, it does a vital role in maintaining homeostasis. The kidneys apart from removing toxic and drugs from the body helps in the regulation of pH by preventing blood plasma from turning too basic or too acidic by regulating ions.  

The kidneys also produce hormones like erythropoietin that instigates the production of red blood cells and renin that assists in monitoring the balance of salt and water and blood pressure in the body.