Correct option is B
The correct answer is (b) 1 April 1951.
The first Five-Year Plan in India started on 1 April 1951.
It was aimed at developing the primary sector, focusing on agriculture, irrigation, and energy.
The plan was based on the Harrod-Domar model and emphasized increasing agricultural production to ensure food security.
The plan marked the beginning of centralized and integrated national economic planning in India.