Oases are small areas in the desert where there is a
a. frequent occurrence of sandstorms
b. water supply that can support vegetation
c. gold mine that supports economic wealth
d. group of cacti that provides food for local animal life

b. water supply that can support vegetation

Explanation:

An oasis is a place of a desert in which you can find water and vegetation. They usually constitute more or less extensive portions of land fertilized by a water source in the middle of the sand. In these places there may be small inhabited settlements, such as those in the Sahara region, the Arabian peninsula or towns such as Pica, in Chile, Ica in Peru or Parras de la Fuente, in Mexico. In addition to giving crops to nearby residents, they serve to supply travelers and caravans.