Adrenergic Agonists Like Epinephrine Are Not Given Orally but Parenterally

Adrenergic agonists like epinephrine are not given orally but parenterally or by inhalation because:

A) They produce toxic by-products in the blood.
B) They are metabolized by the enzyme COMT in the intestinal tract.
C) They are rapidly absorbed by the blood.
D) They are not easily digested in the gastrointestinal tract.