Which one of the following is important strategy for the conservation of biodiversity?

Biosphere reserves are the best answer here. Under UNESCO's Man and Biosphere (MAB) programme, launched in 1971, each reserve has a core area under strict protection, a buffer zone for research and regulated activity, and a transition area where people live and use resources sustainably. That makes it an integrated in-situ strategy that protects biodiversity and supports livelihoods together.

• Botanical Gardens are ex-situ conservation. They keep plants outside their natural habitat, which is useful but not a whole-ecosystem strategy.
• National Parks and Wildlife Sanctuaries are legal categories under the Wild Life (Protection) Act, 1972. They are important in-situ tools, but they are mainly protection-focused with limited human use, so they are narrower than a biosphere reserve.

Mains angle: this connects to the Convention on Biological Diversity (1992) and the in-situ versus ex-situ debate. India now has 18 notified biosphere reserves, so check the latest count if a question asks for it.

Trap: candidates pick National Parks because it is the most familiar protected area, without noticing that the question asks for the broader strategy.