Explanation:

Option A is correct: The Constituent Assembly had 300 members. The members were given vital assistance by two civil servants. One was B. N. Rau, Constitutional Advisor to the Government of India, who prepared a series of background papers based on a close study of the political systems of other countries. The other was the Chief Draftsman, S. N. Mukherjee, who had the ability to put complex proposals in clear legal language. Rajendra Prasad was the President of the Assembly, where he had to steer the discussion along constructive lines while making sure all members had a chance to speak. The lawyer and economist B.R. Ambedkar served as Chairman of the Drafting Committee of the Constitution. Serving with him were two other lawyers, K.M. Munshi from Gujarat and Alladi Krishnaswamy Aiyar from Madras, both of whom gave crucial inputs in the drafting of the Constitution.