Animals Are Totally Dependent on Plants and Microorganisms for Nitrogen

Animals are totally dependent on plants and microorganisms for nitrogen fixation and nitrate assimilation because animals:

A) do not have the reducing power (NADPH) to fix nitrogen.
B) lack the enzyme aminotransferase.
C) lack the enzymes to reduce N₂ and NO₃− to NH₄⁺.
D) lack carbamoyl-phosphate synthetase I.
E) lack glutamate dehydrogenase.