1. The problem is to identify the asymptote of the given exponential decay function graphed. 2. An exponential decay function generally has the form $$y = ab^x$$ where $$0 < b < 1$$ and $$a$$ is the initial value. 3. The horizontal asymptote of an exponential decay function is the line that the graph approaches but never touches as $$x \to \infty$$. 4. From the description, the graph approaches $$y=0$$ as $$x$$ increases, so the horizontal asymptote is $$y=0$$. 5. The open circle at approximately $$(-5,5)$$ suggests the function is not defined or has a hole there, but this does not affect the asymptote. 6. Therefore, the asymptote of the exponential decay function is the horizontal line $$y=0$$. Final answer: The asymptote is $$y=0$$.