An investigation was carried out on two protease enzymes, Protease C and Protease D, to see how pH affects their rate of reaction.

State the optimum pH for Protease D.
Protease C is found in the human stomach. Explain why Protease C is suited to working in the stomach.
Complete the sentences to explain why Protease C does not work at pH 6. Choose words from the following list:
The part of the enzyme that changes shape is the ______.
The change in shape means the enzyme cannot bind to the ______.