Which one among the following statements about the Singareni Collieries Company Limited is correct? (a) Located at Kothagudem in Telangana, this is the first and the oldest coal mining company in India in the private sector (b) It has now diversified into thermal and solar power generation, explosive manufacturing for blasting in opencast mines and consultancy works (c) It has been conferred with 'Navratna' status since 2011 (d) It is the single largest coal producing company in the world