The correct answer is: D. diversity.
A biodiversity hotspot is a region with a high concentration of endemic species, meaning species that are found nowhere else in the world. Hotspots are also regions with high levels of habitat loss and fragmentation, making them particularly vulnerable to extinction.
Rarity is a measure of how common a species is. A species that is rare is one that is found in a small area or has a small population. Endemism is a measure of how unique a species is. An endemic species is one that is found only in a particular area. Critically endangered is a term used to describe a species that is at very high risk of extinction.
Diversity is a measure of the variety of life in a particular area. A diverse area is one that contains many different species of plants and animals. Hotspots are regions of high diversity because they contain many different species of plants and animals that are found nowhere else in the world.