Answer:
In the exponential function y = C(a)^x, the value of a is the base of the exponent, which determines how fast the function grows or decays. If a were equal to zero, then any value of x would result in y being equal to zero, which would make the function flat and unchanging. Therefore, a cannot be equal to zero in an exponential function, as this would result in an undefined or meaningless expression. Additionally, any number raised to the power of zero is equal to 1, so an exponential function with a base of zero would also violate this mathematical rule.