During metabolism, before their conversion to metabolic derivatives, most drugs are acted upon by:

A. amino acids
B. receptors
C. enzymes
D. extracellular fluid

c
Rationale: Most drugs are acted upon by enzymes for conversion to metabolic derivatives during metabolism. This process of biotransformation occurs mostly in the liver. Amino acids and extracellular fluid are not discussed in the text in this capac-ity, and receptors are specific proteins that function at the cellular level.