Answer:
B
Step-by-step explanation:
The answer can't be A because the passage also gives a lot of information about how cacti and plants get water. It can't be C because the passage also focuses on how kangaroo rats get water. It also can't be D because the passage never explains WHY the desert has little water, just that it does.
The answer is B because the passage explains how animals (kangaroo rats) and plants (cacti) survive in the dry desert.