Rice cultivation in Manipur is primarily concentrated in the Imphal Valley. The Imphal Valley is a fertile plain located in the center of the state. It is the most densely populated region of Manipur and is home to the state capital, Imphal. The Imphal Valley is well-suited for rice cultivation due to its warm climate, abundant rainfall, and fertile soil. The valley is also home to a number of rivers, which provide irrigation for the rice fields.
The hilly regions of Manipur are not well-suited for rice cultivation due to their rugged terrain and low rainfall. The river valleys of Manipur are also not ideal for rice cultivation due to their steep slopes and fast-moving rivers. The coastal plains of Manipur are too saline for rice cultivation.
Therefore, the correct answer to the question “Rice cultivation in Manipur is primarily concentrated in: The Imphal Valley / Hilly regions / River valleys / Coastal plains” is The Imphal Valley.