An oasis can be formed by an underground aquifer or river that creates enough pressure for water to seep to the surface, forming the oasis. These aquifers and natural springs allow for life to exist in harsh climates like the desert and are often well known to local herders, farmers, and travelers in the region.
Firstly, an oasis is a small patch of vegetation (Plantlife) surrounded by a desert. Many communities around the area plant strong trees such as palms around outside or perimeter of the oases to keep the desert sand away from the crops and water. Oases are made by a source of a type of fresh water in a dry or arid reigion.
Now, why does it occur? I don't know. Ha... But I do know that it's really beneficial to the community living in that area. But I'll tell you how they're formed. An oasis can be formed by an aquifer or river that creates enough pressure for water to flow past or seep to the surface, forming the oasis. Kind of like a volcano eruption except is a lot more gentle and water instead of magma or lava. These aquifers and springs allow for life to exist in harsh dry climates like the desert...etc.
The real answer is D. Europeans had advanced technology, and they brought disease to the new world. That is why Native americans were overtaken so easily. Hope this helps
