In an exponential decay function, the horizontal asymptote generally represents the value that the function approaches as x approaches positive or negative infinity. For most exponential decay functions of the form \( y = ab^x + k \), where \( b < 1 \), the horizontal asymptote is typically the constant \( k \).
Since the curve intersects the y-axis and given common behavior of exponential decay functions, if we assume it approaches a horizontal asymptote, that value would usually be a non-negative number, most often around y = 0, unless specified otherwise by the graph.
Based on the options provided, and without being able to see the image, the most typical scenario for an exponential decay function would have the horizontal asymptote at \( y = 0 \).
Therefore, the correct response would be:
The horizontal asymptote is at y = 0.