The Constitution of India was enacted by a Constituent Assembly set up:

a) Under the Indian Independence Act, 1947
b) Under the Cabinet Mission Plan
c) Through a resolution of the provisional government
d) By Wavell Plan

Ans-b

Explanation:  Constituent assembly is the body of the representatives which drafts the constitution. It was set up in November 1946 under cabinet mission plan.

Learning: Time line of the constituent assembly:

1934– Idea put forward first time by MN Roy

1935– INC officially demanded it

1938– Jawahar lal Nehru declared that constituent assembly must be made to draft the constitution of free India without outside interference and such assembly be elected on adult franchise.

1940– British Govt officially accepted demand and made ‘August offer’

1942– Crippis proposal for framing of the constitution. Muslim League rejected it and insisted on the partition.

1946– Cabinet mission plan put forward a scheme for constituent assembly which more or less satisfied Muslim league.

Cabinet Mission plan  also proposed a Union of India which was to be empowered to deal with the defense, foreign affairs and communications, recommended undivided India, turned down league’s demand of partition, recognized Indian right to cede from commonwealth, and proposed a weak centre.
Wavell Plan came in June 1945 after end of WW2. It provided for a new executive council at the centre in which all members will be Indians except Viceroy and commander in chief. All portfolios were to be given to Indians except defense. Representation of  ‘highcatehindus’, ‘low caste hindus’, Muslims, Sikhs were to be done on it. It was a failure. It did not had any guarantee of Independence nor it mentioned anything about constituent assembly. Congress and League both rejected on the ground of nomination.

Indian Independence act was based on 3rd june Mountbatten plan which ended the British rule in India making it independent and sovereign state and declared partition of it. It empowered the constituent assembly to frame and adopt any constitution they like. It abolished office of secretary of state, office of viceroy, discontinued appointment to civil services and reservation of posts by secretary of state, designated governor general of India and provisional governors of states as nominal heads of states, ended Britshi paramountcy over princely states and granted them freedom to join either of two dominion or remain independent.