Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to determine your dog's age [title] Look to teeth to determine a puppy's age. [step] If you have a puppy, it's fairly easy to determine its age by examining its teeth. Teeth start developing during a puppy's first year.

Ending1: Most adult dogs mature within two to three years of birth. [substeps] If you find a puppy at a young age or if its teeth are already removed, it could be common dog teeth. Ending2: It might initially throw a tantrum on you-but after 30 to sixty days, it will learn how to relax and age peacefully and happily. [substeps] The shape of a dog's teeth can sometimes change as a kitten grows, especially if its teeth grow at an odd rate. Ending3: You can determine older teeth by looking at the way they get. As the puppy ages, its teeth begin to become smaller and thicker, developing into canines instead of teeth. Ending4: The stage of teeth development is tied to a puppy's approximate age. [substeps] At one month old, teeth will have just started pushing through the gums.

Answer format: ending1/ending2/ending3/ending4