Answer:
the sun or grass
Explanation:
first the sun because the sun helps produce photosynthesis which grows the grass so that other animals can eat from the grass
B is unsustainable as this is a practice of intensive farming usually conducted indoors, and is resource and energy expensive. C is unsustainable because groundwater is a limited resource and groundwater can take 1000s of years to be recharged. D is unsustainable as this involves moving water across vast distances and is expensive and ecologically damaging. A is sustainable as drought-resistant plants would in the long run use less water.
Plants because it can turn it in to something
