Answer:
b. they built an irrigation system for farming.
Step-by-step explanation:
The irrigation system is something big and permanent, made by populations that decided to stabilize and live in the region where the irrigation system was established. This is because, this population wants to start agricultural activities and plant crops that need long times (often) to generate food. In other words, the implantation of an irrigation system means the establishment of agriculture, which is a common characteristic of the population that does not intend to change regions.
In this regard, historians know that the settlers of San Antonio de Bexar intended to make it a permanent settlement because they implemented an irrigation system in the region.