If $0 < b < 1$, what is the horizontal asymptote of $y=ab^t$ as $t \rightarrow \infty$?

Enter NONE if there is no horizontal asymptote (that is, if the graph goes to $\pm \infty$ as $t \rightarrow \infty$). Otherwise enter an equation for the line that is the horizontal asymptote.

The horizontal asymptote has equation help (equations)