The graph shown in the image represents an exponential growth function. In exponential functions of the form $y = a \cdot b^x + c$, the horizontal asymptote typically corresponds to the value of $y = c$, as $x$ approaches negative infinity.

From the graph, we can see that the curve approaches $y = 0$ as $x$ moves towards negative infinity. Therefore, the horizontal asymptote of this exponential function is:

$y = 0$

So, the correct answer is $y = 0$.

Would you like a detailed explanation of how horizontal asymptotes work with exponential functions, or do you have any further questions about this topic?

Here are some related questions you can explore:

1. How does the value of $c$ in an exponential function affect the horizontal asymptote?
2. What is the difference between exponential growth and exponential decay in terms of the asymptote?
3. How do you find the horizontal asymptote of an exponential function algebraically?