Read the short passage given below and answer the question from the following options, that follow according to the passage only:

The main Himalayan river systems are the Ganga, the Indus, and the Brahmaputra river systems. The Himalayan rivers form large basins. Many rivers pass through the Himalayas. These deep valleys with steep rock sides were formed by the down-cutting of the river during the period of the Himalayan uplift. They perform intense erosional activity up the streams and carry a huge load of sand and silt. In the plains, they form large meanders, and a variety of depositional features like flood plains, river cliffs, and levees.

These rivers are perennial as they get water from the rainfall as well as the melting of ice. Nearly all of them create huge plains and are navigable over long distances of their course. These rivers are also harnessed in their upstream catchment area to generate hydroelectricity.

Find out the word from the passage that means "lasting or existing for a long time":