Answer:
natural income
Step-by-step explanation:
Living sustainably in the 21st century means coexisting with the nature. In other words, to live sustainably means to meet the needs of the human without affecting or degrading the mother nature.
In the context, living sustainably means to live from the natural income from the nature's gift to us, using their natural resources and not hurting them or exploiting them. They may be resources from the soil, plants, clean air, animals, nature's clean water,etc.