Which best describes the asymptote of an exponential function of the form F(x) = b^x?
AVertical asymptote at x = 0
BVertical asymptote at x = 1
CHorizontal asymptote at y = 0
DHorizontal asymptote at y = 1
AVertical asymptote at x = 0
BVertical asymptote at x = 1
CHorizontal asymptote at y = 0
DHorizontal asymptote at y = 1