Conservation of plant diversity is mostly a / an

Initially …$A$… biodiversity hot spots were identified but subsequently nine more have been added to the list, bringing the total number of biodiversity hot spot in the world to $\ldots$…$B$… These hot spots are the regions of accelerated habitat loss. Three of these hot spots-Western ghats and Sri Lanka, Indo-Burma and Himalaya, covers our country's, exceptionally high biodiversity regions

Although all the biodiversity hot spots put together covers less than …$C$… $\%$ of the earth's land area, the number of species they collectively harbour is extremely high and the strict protection of these hot spots could reduce the ongoing mass extinctions by almost ..$D$… $\%, A, B, C$ and $D$ in the paragraph refers to

In which of the following, both pairs have correct combination?

Write an explanatory note on Ex situ conservation.