Answer:
D all the way
Step-by-step explanation:
The piece of evidence that would be most relevant to the research question "What actions can we take to protect the manatee population?" would be option D: "Manatees face a new threat as a main food source - seagrass dies off because of poor water quality." This piece of evidence specifically identifies a threat to the manatee population and suggests that actions could be taken to address it.