What is the primary objective of the $Ex-situ$ conservation approach?

$MAB$ stands for

The Earth Summit held in Rio de Janeiro in $1992$ was called:

In the following,each set provides a conservation approach and an example of a method of conservation:
$(a)$ In situ conservation - Biosphere Reserve
$(b)$ Ex situ conservation - Sacred groves
$(c)$ In situ conservation - Seed bank
$(d)$ Ex situ conservation - Cryopreservation
Select the option with the correct match of approach and method.

Which one of the following is related to ex situ conservation of threatened animals and plants?

In your opinion, which is the most effective way to conserve the plant diversity of an area?