Environmentalists are very concerned about the high cost of protecting endangered animals and propose that they should be assessed by assessing the value of various endangered animals to humans. This method is actually not feasible because it is impossible to predict the future value of an animal It is impossible to assess the value of animals that now make an indirect but important contribution to humans. What is the main argument of the author of this passage? ['Protecting endangered animals without value is more important than protecting potentially valuable animals.', 'Although protection of all endangered animals is necessary, it is not economically feasible.', 'Because the method of judging the value of animals to humans is not perfect, the decisions made on this basis are not reliable.', 'Protecting animals of direct value to humans is more important than protecting animals of indirect value.']