Final answer:
The distributions of the three largest kangaroo species in Australia are determined primarily by climate, which affects the availability of resources and habitat suitability, rather than hunting pressure or competition for sites. The correct option is D.
Step-by-step explanation:
The question seeks to identify the factor that determines the distribution of three largest kangaroo species in Australia. Based on the provided information, the correct answer is that the distribution of kangaroo species is primarily determined by climate.
Factors such as hunting pressure and severe competition for den sites may affect populations locally, but changes in climate have had significant historical impacts on species distributions, as seen and other megafauna that experienced population declines due to an inability to find adequate food and habitat changes exacerbated by human hunting.
Species that are found in a limited area, and specifically in Australia, like kangaroos, are known as endemic species. Human hunting has historically contributed to the decline of many species; however, it is not the primary factor determining the current geographical distribution of the largest kangaroo species in Australia.
Instead, their distribution is better correlated with climate factors, which affect the availability of resources and habitat suitability over time. The correct option is D.