Who was the Provisional President of the Constituent Assembly before Dr. Rajendra Prasad took over?

The Constituent Assembly of India held its first sitting on 9 December 1946. As per convention, the oldest member of the Assembly was elected as the temporary/provisional President. Dr. Sachchidananda Sinha, a distinguished parliamentarian from Bihar and the senior-most member, was elected as the Provisional (temporary) President of the Constituent Assembly. On 11 December 1946, Dr. Rajendra Prasad was elected as the permanent President of the Assembly. Hence the correct answer is Dr. Sachchidananda Sinha.