The Constitution of India was adopted by the

Concept

India's Constitution was framed not by the colonial executive or by a legislature already in existence, but by a specially convened, elected constitution-making body. "Adoption" refers to the act of that drafting body formally approving the final text -- a distinct historical step from the text later "coming into force" as law.

Application

Applying this to the four bodies named here:

• Constituent Assembly: first assembled in December 1946 and reconstituted after independence, it worked through a Drafting Committee to prepare, debate, and finalise the constitutional text over nearly three years.

• Governor-General: the Crown-appointed head of the colonial and early dominion executive, an office with no constitution-drafting function.

• British Parliament: the Westminster legislature that had earlier enacted governing statutes for India (such as the Government of India Act, 1935, and the Indian Independence Act, 1947), legislating from London before India framed its own constitution.

• Parliament of India: the legislature created by the constitutional text, so it could only begin functioning once that text had already taken effect.

Only the Constituent Assembly both existed at the right time and had the mandate to frame and approve India's Constitution.

Cross-check

The Constituent Assembly adopted the Constitution on 26 November 1949 (now marked as Constitution Day / Samvidhan Diwas), and the Constitution came into force on 26 January 1950 -- the two-month gap between "adoption" and "commencement" is itself a commonly tested distinction, and it confirms adoption was an act of the Assembly, not of the post-1950 Parliament that the same document later created.