The three-day budget session of Goa Assembly begins today. Protem Speaker Mahadev Naik will administer the oath of office to the newly elected MLAs today.Governor K Sankaranarayanan will address the house tomorrow, while Chief Minister Manohar Parrikar who also holds the Finance portfolio, will present the budget for the financial year 2012-13 on Wednesday.In the meanwhile, the Congress Legislature Party yesterday elected unanimously the former Speaker Pratapsingh Rane as the leader of opposition.