Question

select the running freshwater ecosystem.
this ecosystem has:

• a mix of fresh and salty water
• muddy soil that is rich in nutrients
• many different types of organisms

this ecosystem has:

• water that is low in salt and rich in oxygen
• flowing water
• organisms that swim or stick to rocks

this ecosystem has:

• land that is covered with water for most of the year
• many grasses and few trees
• soil that is rich in nutrients

Explanation:

A running freshwater ecosystem has flowing water. The second ecosystem description mentions "flowing water", while the first has a mix of fresh and salty water (more like an estuary) and the third has land covered with water most of the year (more like a wetland).

Answer:

The second ecosystem (with flowing water, low - salt and oxygen - rich water, and organisms that swim or stick to rocks) is the running freshwater ecosystem.