(D) Signing of Constitution by the Constituent Assembly: On November 26, 1949, the Constitution of India was adopted and signed by the members of the Constituent Assembly, marking a key step in its implementation.
(A) Formation of the Drafting Committee: The Drafting Committee was formed much earlier, and hence this is incorrect.
(B) Commencement of the Constituent Assembly: The Constituent Assembly had commenced its proceedings much before November 26, 1949, and so this option is also incorrect.
(C) Designing of the National Flag of India: The National Flag of India was adopted on July 22, 1947, therefore this option is also incorrect.