Final answer:
The Aztecs used chinampas, or floating gardens, to farm more productively by controlling soil fertility and watering, effectively supporting a high population density around their capital of Tenochtitlán. Option C.
Step-by-step explanation:
The invention that helped the Aztec farm more productively was c. Chinampas.
Chinampas were raised planting beds constructed on floating platforms in Lake Texcoco, which surrounded the Aztec capital of Tenochtitlán.
This agriculture technique allowed Aztec farmers to thoroughly control soil fertility and watering, resulting in remarkable productivity that could support a high population density.
The chinampas system was more efficient compared to other contemporary agricultural methods, supporting six people per acre in the fifteenth century, whereas the most successful technique in Europe and Asia at the time, Chinese intensive rice farming, supported only about one person per acre.
The Aztec state relied on the surplus food produced by these floating gardens to feed the urban classes of craftspeople, warriors, bureaucrats, and nobles.
By using chinampas, the Aztecs successfully managed intensive agriculture, particularly maize, which was a fundamental part of their culture and economy.
Hence, the right answer is option C.