Which function has a horizontal asymptote of y is equal to 3 ?

An exponential function of the form a·b^x + k has horizontal asymptote y = k, because the exponential term approaches 0 in one direction. Choice C adds 3, so its horizontal asymptote is y = 3; the other choices have no vertical shift that gives an asymptote of 3.

AI-written and checked against the verified answer.