Answer: Option A
Answer: (a)
Narmada is the only river in India that flows in a rift valley, flowing west between the Satpura and Vindhya ranges. The Tapti River and Mahi River also flow through rift valleys, but between different ranges.
One theory is that the area in which the fossils are located, i.e., the Narmada Valley near Mandla, was actually a deep inundation of the sea into peninsular India till the Post- Cambrian Tertiary age, about 40 million years ago.
This means that Narmada was a very short river that terminated in the inland sea above Mandla and that the recession of the sea caused geological disturbances, which created the present rift valley through which the Narmada River and Tapti River flow in their present journey to the Arabian Sea.