The correct answer is D. The faster the stream flows, the more diverse its organisms are.
The flow rate of streams can affect the types of organisms that live in them. In general, faster-flowing streams tend to have more diverse communities of organisms than slower-moving streams. This is because fast-moving water can support a wider variety of species, including those that require high oxygen levels and those that are adapted to withstand the force of the water. Slower-moving streams, on the other hand, may have fewer species and are often dominated by plants, algae, and other organisms that can thrive in low-oxygen environments.
Therefore, option D is the best description of the relationship between the flow rate of streams and the types of organisms that live in them.