The Brahmaputra, which existed before the Himalayas rose and kept cutting its valley as they were uplifted, is an example of:

An antecedent river (or antecedent drainage) is one that existed before the uplift of the land (such as a mountain range) across its path. As the land slowly rose, the river kept cutting down its bed at the same pace, maintaining its original course. This creates deep gorges across the mountains.

Examples in India:

The Indus, the Sutlej and the Brahmaputra are classic examples of antecedent rivers. They are older than the Himalayas and rise in Tibet, north of the Greater Himalaya.

As the Himalayas were uplifted, these rivers cut deep gorges through them. Examples include the Indus gorge near Gilgit, the Sutlej gorge near Shipki La, and the Brahmaputra's gorge around the great bend near Namcha Barwa.

The Arun and Kosi in Nepal are also considered antecedent.

How to recognise antecedent drainage:

• The river cuts across a mountain range rather than flowing around it.
• It forms deep, narrow gorges where it crosses the range.
• Its source lies beyond (behind) the main mountain range.

A related type based on origin:

Superimposed drainage: rivers that develop on a cover of younger rocks and then cut down into older rocks with a different structure, keeping their original course. The Damodar, Subarnarekha, Chambal and Banas are sometimes given as Indian examples.

Patterns of drainage (shape):

Dendritic (tree-like), trellis, radial and rectangular patterns describe the shape formed by rivers and their tributaries, rather than their age relative to the land.

Importance:

Antecedent rivers provide routes through mountains and sites for hydroelectric projects, though their gorges are prone to landslides and floods.

Why not the other options?

• ✗Superimposed drainage is inherited from an overlying rock cover.
• ✗Dendritic is a tree-like pattern, not a type based on origin.
• ✗Trellis is also a pattern, not a type based on origin.