The horizon line is typically defined as the point where the sky meets the ground or where the viewer perceives that the earth's surface is meeting the sky. In the context of your options, none of them specifically states "where the sky meets the ground," but the most relevant choice would likely be related to the overall landscape.
If the image primarily displays a mountain and its surroundings, the best option may be:
the bottom of the mountain with trees
This option suggests a ground-level perspective where the horizon line would be positioned. However, if the context of the image indicates that the actual horizon line lies at a different level (for instance, at the top of the mountain), then that could also fit depending on the visual context.
For clarity's sake, please confirm the context of your image to better identify the horizon line.