Environmental scientists are concerned about the high cost of protecting endangered animals and propose that the value of various endangered animals to humans should be determined to determine which animal to protect. This method is not practical because it predicts the future value of an animal It is impossible to evaluate the value of animals that now make an indirect but important contribution to humans. In the following items, which of the following is the author's main argument? ['Protecting endangered animals without value is more important than protecting potentially valuable animals.', 'Although it is necessary to protect all endangered animals, it is not economically feasible.', 'Decisions made on this basis are not reliable because the method of judging the value of animals to humans is not perfect.', 'It is impossible to assess whether endangered animals are important to humans.']