【单选题】All of the nitrogen-containing compounds of the human body are synthesized from amino acids. Which one of the following statements about amino acid degradation is correct?
A.
Amino acid carbons can be stored only as glycogen.
B.
The liver is the only site of amino acid oxidation.
C.
The nitrogen of oxidized branched-chain amino acids must travel to the liver for disposal.
D.
The nitrogen of amino acids is always excreted as urea.
E.
The nitrogen of amino acids is only excreted by the kidney.