All of the provided options can contribute to the small gene pool of cheetahs today, but the correct answer would be "inbreeding in zoos". Inbreeding refers to the mating of closely related individuals, which reduces genetic diversity and increases the risk of genetic disorders and diseases. Cheetahs in captivity, particularly in zoos, often have limited breeding options and have resorted to inbreeding, which has resulted in a smaller gene pool and increased the vulnerability of the species to potential threats.
