Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to introduce a new dog to your senior dog [title] Keep your senior dog visually separate from your new dog. [step] Place their cages at opposite ends of the house and keep them entirely separate for the first few days. During this period, you should take measures to make sure your senior dog does not see the new dog.

Ending1: Similarly, make sure the dogs do not come near each other during their first two days of quarantine. [title] Introduce the dog to its new home. Ending2: For example, you should not let them both out of the house at the same time and should keep them in different parts of the house. [title] Introduce your senior dog to the new dog via scent. Ending3: Keeping them separated can make the process much easier. Be sure to keep the dogs occupied during both periods so they do not see one another. Ending4: [substeps] Place the dog in both kennels and eliminate their use of the block. Alternately, put them in separate rooms across the house.

Answer format: ending1/ending2/ending3/ending4