Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to get dogs to mate [title] Wait until your dog is old enough. [step] Just like human beings, dogs need to reach biological sexual maturity before it's medically safe for them to breed. This is especially important for the female dog, as her health might be put at risk by a pregnancy her body is not prepared to carry.

Ending1: It's generally a good idea to wait until your dog is old enough to have sex. [substeps] You can even wait until your dog is 18 or older, so that she can fully mature and have some dating power and sex. Ending2: [substeps] A male dog should be at least 1.5 years of age before breeding. A female dog should be on her second or third heat cycle. Ending3: [substeps] You'll also have to wait until your dog is at least six months old, ideally on average, to breed. Talk to your vet to make sure you'll need at least a puppy for breeding. Ending4: Once your dog reaches sexual maturity, it is appropriate to begin training your dog. If you wait too long and your dog hasn't reached sexual maturity yet, the two dogs may begin to breed in the process.

Answer format: ending1/ending2/ending3/ending4