A) Ex-situ conservation is done by preserving the components of biological diversity outside their natural habitats. It is done by conserving genetic resources, as well as wild and cultivated or species. Examples include gene banks, microbial cultures, botanical gardens, etc.
B) In-situ conservation is done by conserving the species in their natural habitats. It is the best way of biodiversity conservation. Examples include sacred groves, national parks, biosphere reserves, sanctuaries, etc.
So, the correct answer is 'Botanical gardens'.