Which one of the following biosphere reserves is spread over three States in India?

The Nilgiri Biosphere Reserve is the largest biosphere reserve in India and spans three states — Tamil Nadu, Kerala, and Karnataka. It includes major protected areas such as Mudumalai, Bandipur, Nagarhole, Mukurthi, Silent Valley and Wayanad. Achanakmar-Amarkantak spans Chhattisgarh and Madhya Pradesh (two states), Seshachalam lies entirely in Andhra Pradesh, and Agasthyamalai spans Kerala and Tamil Nadu (two states). Hence Nilgiri is the only biosphere reserve among these spread over three states.