Which clue is most useful for identifying Dun valleys?

Correct answer: Long valleys between Shiwalik and Himachal

The direct answer is C: long valleys between Shiwalik and Himachal. A Dun is a longitudinal valley in the Himalayan foothill region. It generally lies between the outer Shiwalik range in the south and the Lesser Himalaya, or Himachal, in the north. Dehra Dun is a familiar example. Option C is correct because it gives both the location and the elongated shape that identify a Dun valley. Option A is wrong because the permanent snowline belongs to the high Himadri region, not to a Dun valley. Option B is wrong because a Bay of Bengal delta is a coastal depositional feature formed by a river, not a Himalayan valley. Option D is wrong because crescent dunes are wind-made landforms of deserts such as the Thar. Memory cue: Dun = valley between Shiwalik and Himachal; Dehra Dun is the name clue.