I think that that the answer should be C asexual reproduction of a single-celled organism
They're called anastomoses
This is the answer
I have to have 20 characters so...
I know they carry diseases which can harm or kill the animal it is attached to. These diseases can taint the meat of the animal so it wouldn't be wise to eat it which stinks if the animal is bread for eating. They can also irritate the skin and cause rashes, or even eat the flesh of the animal away.
Natural selection is when certain environmental qualities cause a species to evolve in order to survive in the environment. Natural selection is a specific part of that, when some of the variations of the species die off because they can't survive, then the ones who survive live to create more living babies with the qualities that allow them to survive in the environment.