Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to know if a male dog is fertile [title] Make sure that your dog is old enough to breed. [step] A male dog that is too young will not be able to reproduce. A male dog usually reaches sexual maturity when they are over a year old, however they usually begin puberty when they are six months to eight months old.

Ending1: [title] Be sure your dog is healthy enough to have a litter. [step] The correct outcome to obtain a male dog is a dose of 3 or more viable puppies that have not yet been neutered. Ending2: Older dogs, like their peers, may develop fetuses or larger, serious testicles. [title] Research the characteristics of your male dog. Ending3: [substeps] If a female dog has had a male dog in the past, there is no guarantee that they will be able to breed. It is important to follow you specific plan. Ending4: They can impregnate a female dog from the point of puberty on. [substeps] If you want to use your dog for breeding when it is at its maximum fertility, wait until it is at least a year and a half old.

Answer format: ending1/ending2/ending3/ending4