Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to exercise your puppy [title] Let your pup explore the backyard. [step] For puppies under 12-18 months of age, self-directed play will fulfill your puppy's exercise needs. In other words, the majority of your puppy's exercise should be exploring, digging, and free play.

Ending1: [substeps] Having exercise nearby is an excellent way to get your pup accustomed to the outdoors. If you have an outdoor backyard, take your dog for short walks around it. Ending2: Therefore, let your puppy roam around your backyard, or an enclosed grassy area that is safe. [substeps] While your puppy is exploring, supervise your puppy to ensure that it is safe at all times. Ending3: If you do not have an outdoor area, get your dog to () the area you want, then let him move around on the floor. [substeps] Do not let your dog play in grass. Ending4: Reducing the amount of play your pup does can also help strengthen his muscles and reduce the chance of injuries. [substeps] For younger puppies, larger spaces may offer a cool-down.

Answer format: ending1/ending2/ending3/ending4