Schistosomiasis is a surface infectious disease, caused by pathogens that invade the human body through the skin, and is mainly transmitted by contact.

① adult schistosomes in the human body mating, egg-laying;

② schistosome eggs fall into the water with human feces, after a certain period of time, the eggs hatch out of the trichinae, the trichinae can be movement;

③ when encountered in the water of a kind of snail called "nails snail", the trichinae that is, from the outwardly protruding molluscular part of the burrow, and the development of reproduction in the body of the nail snail, and the development and reproduction of the body of the snail.

③ When encountering a snail in the water called the "nail snail", the trichinae will bore into the water from its soft body part extending outward and develop and multiply into a large number of tailed larvae in the body of the nail snail;

④ When the nail snail is crawling in the water or on the plant stems and leaves with water droplets, the mature tailed larvae will leave the body of the snail to enter into the water;

⑤ If a person goes into the water or walks on the ridge of the countryside in bare feet, the tailed larvae will invade into human body through the skin and develop into adult worms in the body of the person.

Only B is correct.

Therefore, B.