Explanation:

- The valleys between the lesser Himalaya and Shiwaliks are indeed known as Duns. They are long, narrow valleys known for their fertility and beauty.

- Marg generally refers to a highland pasture, specifically in areas like Kashmir, unrelated to these valleys.

- Bet is not commonly used to describe valleys between these specific ranges.

- Tarai is a region characterized by marshy grasslands, directly adjacent to the foothills of the Himalayas but is distinct from Duns.