This region' s swimmers generally swim during the day because they are too afraid of sharks to swim after dark but feel safe swimming during daylight hours. Yet all recent shark attacks on swimmers in the area have occurred during the day, indicating that, contrary to popular opinion, it is not more dangerous to swim here at night than during the day. The reasoning in the argument is most vulnerable to criticism on the grounds that it ['presumes, without providing justification, that swimmers cannot be the most knowledgeable about which times of day are safest for swimming', 'overlooks the possibility that some sharks are primarily nocturnal hunters', "overlooks the possibility that swimmers might feel anxiety caused by not being able to see one's surroundings in the dark", 'fails to take into account the possibility that the number of shark attacks at night would increase dramatically if more people swam at night']