Answer:
Grow plants
Explanation:
A plain is a large flat land used for culture. In the plains of Mojo in actual Bolivia, there is no lake or any major water stream in which to fish.
Since it's a plain, there is no mountains or any other massive rock structure to carve monoliths from.
Although you could weave fabric with some plants, the people of Tiahuanacu didn't and most likely used wool from the alpacas and llamas of the area to weave their fabrics.
