Identify the correct statement regarding enzymes.

• A
  Enzymes are specific biological catalysts that can normally function at very high temperatures $(T > 1000 \; K)$.
• B
  Enzymes are normally heterogeneous catalysts that are very specific in their action.
• C
  Enzymes are specific biological catalysts that cannot be poisoned.
• D
  Enzymes are specific biological catalysts that possess well-defined active sites.