Why is it useful to study Tapi with Narmada?

Correct answer: Both are west-flowing peninsular rivers

Narmada and Tapi are both important Peninsular rivers with a westward course. They flow through rift-valley regions and finally enter the Arabian Sea, unlike most major Peninsular rivers that flow eastward toward the Bay of Bengal. Studying them together highlights this shared drainage direction and geographical setting.

Option D is correct because both are west-flowing Peninsular rivers. They are not northern tributaries of the Ganga, Himalayan-origin rivers, or rivers that form deltas in the Bay of Bengal. Although the two rivers have different sources and courses, their common westward flow into the Arabian Sea makes them a useful pair for comparison.