Answer:sunlight on the other side of a fence
Explanation: The phenomena to exhibit a response is called Phototropism. Plants like other autothrops manufacture their own food through the process of photosynthesis, to do this, they need to water, carbon dioxide, and minerals in the presence of sunlight. Phototropism occurs when plants grow towards a source of light.
Therefore sunlight on the other side of a fence is the only cue from the options that can make a plant to respond.