Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to tell if your dog is in heat [title] Understand the basic reproductive cycle of your dog. [step] When wondering if your dog is in heat, it first helps to understand her normal hormonal cycle. When a female dog reaches maturity, and is physically ready to reproduce, her estrogen levels increase, initiating the release of eggs from her ovaries.

Ending1: At that point, heat lamps, lighters, burners, and scented candles will glow, leading to her body turning dark. If in doubt, put your dog in a smoke-room to get air into her intakes. Ending2: [substeps] Young puppies are considered fertile for about 24 hours. Kittens, up to 5 years old, are considered fertile again for at least 2 days. Ending3: As a result, she may become more eager to have children, especially when menstruating. In an average sized dog, her brain and body produce large amounts of estrogen. Ending4: If mating occurs during this period, the eggs can then be fertilized and an embryo can be produced. [substeps] Female dogs, will generally go into heat during puberty, at around 6 to 24 months of age depending on breed.

Answer format: ending1/ending2/ending3/ending4