Correct Answer: (b) Vasuki
Note: The churning of the ocean of milk (Ksira Sagar) was an elaborate process. Mount Mandara or Mandar Parvat was used as the churning rod and Vasuki, the king of serpents who abides on Shiva's neck, became the churning rope. Lord Vishnu, in the form of Kurma Avtar, came of their rescue and supported the mountain on his back.