Which factor is important in the development of inland drainage in the Thar region?

Correct answer: Low rainfall and sandy arid basins

The direct answer is option A, low rainfall and sandy arid basins. Inland drainage means that a river or stream does not reach the sea; it may disappear into sand, end in a lake, or lose its water through evaporation and seepage. The Thar region is very dry, receives little and irregular rainfall, and contains sandy surfaces and shallow or enclosed basins. These conditions prevent many streams from forming a continuous channel to the sea. Luni is a familiar example: it flows through Rajasthan and its water may spread or disappear in the dry region. Option A is correct because low rainfall and arid sandy basins encourage inland drainage. Option B, permanent glaciers and a deep gulf, does not describe the hot desert Thar. Option C, very long east-flowing rivers, would carry water towards the Bay of Bengal rather than produce inland drainage. Option D, a dense mangrove delta, is a wet coastal environment formed near a river mouth, not an arid interior basin. Memory cue: dry desert plus disappearing stream equals inland drainage; connect Luni with the Thar.