When Protein Molecules Are Used as Energy Sources, the Amino

When protein molecules are used as energy sources, the amino groups of the amino acids are ____ and the carbon backbones enter ____.

A) excreted as free amino groups (-NH₂) ; glycolysis
B) build new proteins; the electron transfer chain
C) excreted as ammonia (NH₃) ; the citric acid cycle
D) used to synthesize nucleic acids; glycolysis
E) converted to glycogen; citric acid cycle