The correct option is A Core zone
Biosphere reserves are the sites in an ecosystem where the plants and animals in the ecosystem are protected for biodiversity conservation.
They are divide into three zones,
1. Core zone - This area is undisturbed and legally protected. No human activity is allowed here.
2. Buffer zone - It surrounds the core area. Limited human activity is allowed here for research and education.
3. Transition zone - It is the outermost or peripheral part of the reserve where reserve management and local people cooperate for activities like cropping, recreation etc. without disturbing the ecoystem.