One of the ex-situ conservation methods for endangered species is
A) Wildlife sanctuaries
B) Biosphere reserves
C) Cryopreservation/ seed bank
D) National parks

Hint: The species that are likely to become extinct in near future are known as endangered species. They are at risk due to habitat loss, poaching and invasive species. There are many laws that restrict land development, forbid hunting. There are two basic conservation strategies- ex-situ and in situ conservation.

Complete answer:
Ex-situ conservation is the process of removing part of population from a threatened habitat and placing it in a new location to protect endangered species.
Ex-situ management can occur within or outside a species natural geographic range.
Zoo, aquarium, seed bank are the methods of ex-situ conservation.
Cryopreservation is the ex-situ method for plants. It involves the storage of seeds, pollen or embryos in liquid nitrogen.
Conservation of livestock genetics can also be done with the help of cryopreservation.
Cryopreservation is used for indefinite storage of material over a much greater time period.
The conservation of ecosystems and natural habitats and the recovery of viable populations of species in their natural surroundings is called as in situ conservation.
Example of in situ conservation – national parks, biosphere reserves and sanctuaries.

So the correct answer is cryopreservation/seed bank.

Note:The basic difference between the in situ and ex situ conservation is the habitat place where the process is carried out. In situ conservation provides greater mobility to the animal species because of large habitat area whereas ex-situ provides less mobility to organisms. The ex-situ is a method of conservation of organisms outside the natural environment through genetic conservation.