The correct answer is option 3, Constituent Assembly. The Constituent Assembly of India was responsible for drafting the Constitution of India, and it was this assembly that elected Dr. Rajendra Prasad as the first President of India. The Constituent Assembly was made up of representatives from various regions and communities across India. These representatives were elected by the members of the provincial legislatures, who were themselves elected by the people of India. The Electoral College, mentioned in option 1, is a term used to refer to a group of individuals who are responsible for electing a president or other high-ranking officials. While the Electoral College did play a role in the election of the President, it was the Constituent Assembly that ultimately made the decision.