At the start of an enzyme-catalyzed reaction, which of the following is true about the concentrations of the reactants and products?

• A. Free enzyme concentration is low, and product concentration is high.
• B. Enzyme-substrate complex concentration is high, and free substrate concentration is low.
• C. Product concentration is high, and free enzyme concentration is low.
• D. Free substrate concentration is high, and enzyme-substrate complex concentration is low.

Answer: (D)