Option (B) The Narmada is the correct answer. The Narmada river flows in a rift valley formed between the Vindhyan and Satpura ranges. This is a distinctive characteristic of the Narmada river, which is part of the Peninsular drainage system. Unlike the Himalayan rivers mentioned in the context that form V-shaped valleys and gorges through erosional activity, the Narmada flows through a structural rift valley. The other options—The Son, The Yamuna, and The Luni—are not known for flowing in rift valleys. The Yamuna is a Himalayan river (tributary of Ganga), the Son is a peninsular river but not in a rift valley, and the Luni flows in the arid region of Rajasthan.