A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that __________.

• A. the hydrogen bonds that define the structure of the enzyme's active site are unstable
• B. the substrate becomes a competitive inhibitor at lower temperature
• C. the enzyme was denatured
• D. the cofactors required by the enzyme system lack the thermal energy required to activate the enzyme
• E. there is too little activation energy available