One of the ex situ conservation methods for endangered species is
(a) wildlife sanctuaries
(b) biosphere reserves
(d) national parks.
(c) : Ex situ conservation is the preservation of components of biological diversity outside their natural habitats for example: in zoos, aquaria, botanical gardens and gene banks. They are the most conventional methods of ex-situ conservation, all of which house whole, protected specimens for breeding and reintroduction into the wild when necessary and possible. Rest of the given options are examples of in situ conservation.