The effect of pH on enzyme activity is characterized by（ ）

A、Each enzyme has its optimum pH
B、The farther away from the optimum pH of the enzyme, the lower the activity of the enzyme
C、Peracid or overbase can inactivate the enzyme
D、The optimum pH of the same enzyme may vary depending on the type and concentration of the substrate
E、The same pH of the same enzyme is a fixed value