The development of agriculture in South America was primarily affected by factors such as the domestication of plants and animals, changes in climate, and the movement of populations. Among the options you provided, the most relevant one would be A: more people moved to the Gran Chaco.
The movement of people to areas like the Gran Chaco could lead to increased agricultural practices as populations settle and interact with the environment, adapting to and utilizing local resources for farming. The other options, while they may represent societal changes, do not directly contribute to the development of agriculture in the same way.