Some visitors to the park engage in practices that seriously harm the animals  Surely, no one who knew that these practices seriously harm the animals would engage in them
So it must be concluded that some of the visitors do not know that these practices seriously harm the animals
Some of the people polled live outside the city limits. However, no one who can vote in city elections lives outside the city. Ttherefore some of the people polled cannot vote in the upcoming city election.