Answer : 2. "Elected by the Legislative Assemblies of different provinces "
Explanation :

The Constituent Assembly was constituted in November 1946 under the scheme formulated by the Cabinet Mission Plan. The total strength of the Constituent Assembly was to be 389. Of these, 296 seats were to be allotted to British India and 93 to Princely States. Out of 296 seats allotted to British India, 292 members were to be drawn from the eleven Governors’ provinces and four from Chief Commissioners’ Provinces, one from each.