Step 1: Historical background.
The Constituent Assembly of India was formed to draft the Constitution of India. It was created after the Cabinet Mission Plan of 1946.
Step 2: Analyzing the options.
(A) 1945: Incorrect — no such assembly existed then.
(B) 1946: Correct — the Constituent Assembly was formed in December 1946.
(C) 1947: This was the year of independence, but the assembly had already been formed.
(D) 1948: By 1948, the Constituent Assembly was already functioning.
Step 3: Conclusion.
Thus, the Constituent Assembly was formed in 1946.