Capuchin monkeys in Venezuela often rub a certain type of millipede into their fur. Secretions of these millipedes have been shown to contain two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate the capuchins. The rubbing behavior is rare except during the rainy season, when mosquito populations are at their peak. Ttherefore, the monkeys probably rub the millipedes into their fur because doing so helps protect them against mosquitoes. Which of the following would it be most useful to determine in order to evaluate the argument? ['Whether the two chemicals provide any protection for the millipedes against their own predators', 'Whether animals other than capuchins rub insects of any kind into their fur', 'Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world', 'Whether the only time the millipedes are readily available to the capuchins is during the rainy season']