A park in France is going to "recruit" a group of crows as "cleaners". But some people also doubt whether these "crow cleaners" can work. If the following items are true, which most supports these people's doubts are:. ['"Crow cleaners" may cause people\'s curiosity, leading to a sharp increase in park visitors and thus more garbage.', 'Through experiments, the trained "crow cleaners" can only pick up extremely limited light and small garbage every day, which has almost no cleaning effect on the park.', 'According to survey statistics, in order to see how the "crow cleaners" pick up garbage, most tourists tend to intentionally throw a lot of garbage.', 'Even a trained crow still retains the instinct of clumsy branches, small stones, and the crow itself will generate garbage.']