Determine whether y=4(7)^x represents an exponential function. Explain why the equation does or does not represent an exponential function.
A: It is a linear function.
B: It fits the pattern y=ab^x.
C: The exponent is a constant.
D: Although it fits the pattern y=ab^x, b cannot be 1.
E: Although it fits the pattern y=ab^x, b cannot be negative.