Final answer:
The 'floating islands' used in ancient civilizations, known as chinampas, were agricultural platforms for farmland, which allowed the Aztecs to efficiently produce crops by controlling soil fertility and irrigation.
c) Chinampas; farmland is correct option.
Step-by-step explanation:
The "floating islands" referred to in ancient civilizations are known as chinampas, which were used for farmland. The Aztecs notably utilized chinampas by creating raised planting beds on floating platforms in Lake Texcoco. This ingenious method allowed them to control soil fertility and provided an efficient irrigation system to maximize agricultural output, even within the constraints of a lacustrine environment.
Using chinampas, the Aztecs were able to support a dense population by producing a significant amount of food per acre, securing the sustenance of their large urban population concentrated in the capital, Tenochtitlán.