The exponential functions have a horizontal asymptote. Unless there is no vertical shift in the function, the asymptote is the x-axis. The equation of x-axis is y = 0.
Since there is no vertical shift in the given exponential function, its asymptote will be y = 0.
Exponential functions do not have vertical asymptotes.
So the correct answer is Option D. Horizontal asymptote y = 0
