Which one of the following is included in the world list of biosphere reserves by UNESCO?
(a) Kinnaur Region
(b) Spiti Valley
(c) Nallamalai Hills
(d) Sunderbans
(d) The Sundarbans is the largest single block of tidal halophytic mangrove forest in the world. The Sundarban forest lies in the vast delta on the Bay of Bengal formed by the super confluence of the Ganges, Padma, Brahmaputra and Meghna rivers across southern Bangladesh. It is a UNESCO World Heritage Site.