Which Article of the Indian Constitution did Dr. B.R. Ambedkar term as the ‘Heart and Soul of the Indian Constitution’?

Which Article of the Indian Constitution did Dr. B.R. Ambedkar term as the ‘Heart and Soul of the Indian Constitution’? [SSC Graduate Level Exam 19/05/2013]

          a) Article 14

          b) Article 19

          c) Article 356

          d) Article 32