The piece of evidence that best supports the claim "Gardeners should never use pesticides on their plants" is:
Pets and children often play in and around gardens, where they can be exposed to pesticides.
This evidence supports the claim because it highlights the potential harm that pesticides can pose to pets and children who come into contact with them. Since pets and children frequently interact with gardens, using pesticides can increase the risk of exposing them to harmful chemicals. This aligns with the idea that gardeners should avoid pesticides to prioritize the safety and well-being of both pets and children.