Answer:
D. They live in freshwater, are free-living and reproduce sexually and asexually.
Explanation:
Most planarians are found in freshwater. Since they reproduce through fission, they reproduce asexually. However, since they are heteromorphic, they also reproduce sexually.
A river or steam / moving body of water
No because they already have a kingdom
A flagellum, is a structure in single celled organisms that pave the way for movement. In sperm cells for example, they can transport themselves so quickly due to the rapid movement of the flagellum.
Hope this helped.