Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to teach your dog to bolt from a standing start [title] Make sure your dog is capable of this trick. [step] Bolting from a standing start requires that your dog is healthy and active so that he can run at a fast pace. Old or sick dogs may not be able to master this trick.

Ending1: [title] Have a trainer help you teach your dog this trick. [step] Most training programs require that you have a trainer stand your dog down in the sitting room. Ending2: [substeps] It also helps if your dog has an energetic personality. Dogs who love to play chase or catch are often good candidates for this trick. Ending3: Opt for a younger dog if possible to increase the chances of him learning this trick. [substeps] Older dogs tend to have more skills in certain areas, like jumping. Ending4: [substeps] You do not want to find a dog who cannot do this trick at home. It's best to get an older dog or dog who is " certified " by a veterinarian.

Answer format: ending1/ending2/ending3/ending4