Final answer:
Among the choices provided, D. f(x) = -(-5)^x is an example of an exponential function, because it has a constant base raised to a variable exponent, which is the defining characteristic of an exponential function.
Step-by-step explanation:
The question asks to identify which of the given functions represents an exponential function. An exponential function is defined as a mathematical expression where a constant base is raised to a variable exponent. Looking at the provided options, D. f(x) = -(-5)^x is the correct answer. This is because it fits the form of an exponential function, which generally looks like f(x) = a*b^x, where a is a constant, b is the base (>0, and b≠1), and x is the exponent.
Options A, B, and C do not represent exponential functions. A is a constant function, B is a cubic function, and C is a linear function. Therefore, the only exponential function among the choices is option D.