The most accurate answer to why some groups in South America continued to live as nomads after the development of agriculture is:
A) they lived in ecosystems that were not suitable for farming.
Many nomadic groups thrived in regions where the environment was not conducive to agriculture, such as arid deserts, dense forests, or mountainous areas. These ecosystems often provided ample resources for a foraging lifestyle, making it unnecessary for them to adopt farming practices. While options C and D may reflect certain cultural perspectives or resource availability, A is the most fitting explanation in a broader ecological context.