What happens as a river gets older apex

The gradient smooth ens...the waterfalls and the rapids gradually disappears

It has low gradient and low erosive energy

Explanation:

A river can be defined as the natural flow of water course, which is usually a source of water. This water flows towards the another river, ocean or sea.

A older river usually has very low gradient and low erosive energy. They also have flood plains.

Example of older rivers are : Yellow, Nile, lower Ganges, et cetera.

"a.) well–developed vascular system."

i think its through the fallopian tube