What is the definition of a tributary?

A tributary is a river or stream flowing into a larger river or lake. It is also a person or state that pays tribute to another state or ruler.

1. a river or stream flowing into a larger river or lake.

"the Illinois River, a tributary of the Mississippi"

2. a person or state that pays tribute to another state or ruler.

"tributaries of the Ottoman Empire"

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

the cell cycle is the final answer! : )