What are the islands of the desert called?

The correct answer highlights that desert oases are often referred to as the "islands of the desert." These oases are vital water sources in arid environments, providing essential habitat for both vegetation and various forms of wildlife. They typically consist of fertile land found in the midst of otherwise inhospitable desert conditions, where natural springs or underground water sources allow plants and trees to flourish. This contrast creates a micro-ecosystem that offers shade and sustenance in an otherwise harsh environment, much like islands do in an ocean.

The other options describe different geological features or formations, but they do not capture the essence of a fertile area surrounded by desert. Rocky outcrops refer to exposed rock formations that might rise above the surrounding desert, while mountain ranges signify substantial elevations which can also exist in desert regions without necessarily providing the same biological diversity or water availability as oases. Sand dunes are formations created by wind-sculpted sand and do not represent areas of sustenance or water, contrasting sharply with the characteristics of an oasis.