The correct answer is Option 1 - 9 December 1946
On 9 December Constituent Assembly began its sessions.
Major events of 1946:
16 May 1946: Cabinet Mission announces its constitutional scheme
16 June 1946: Muslim League accepts Cabinet Mission’s constitutional scheme
16 June 1946: Cabinet Mission presents a scheme for the formation of an Interim Government at the Centre
16 August 1946: Muslim League announces Direct Action Day
2 September 1946: Congress forms Interim Government with Nehru as the Vice-President
13 October 1946: The Muslim League decides to join the Interim Government
3-6 December 1946: British Prime Minister, Attlee, meets some Indian leaders; talks fail
9 December 1946: Constituent Assembly begins its sessions. | 
