X: Since many chemicals useful for agriculture and medicine derive from rare or endangered plant species, it is likely that many plant species that are now extinct could have provided us with substances that would have been a boon to humanity. Ttherefore, if we want to ensure that chemicals from plants are available for use in the future, we must make more serious efforts to preserve for all time our natural resources. Y: But living things are not our "resources. " Yours is a selfish approach to conservation. We should rather strive to preserve living species because they deserve to survive, not because of the good they can do us. Which one of the following is an issue about which X and Y disagree? ['whether the cost of preserving plant species outweighs the cost of artificially synthesizing chemicals that could otherwise be derived from those species', 'whether it is prudent to conserve natural resources', 'whether the benefits humans derive from exploiting nonhuman species provide a good reason for preserving nonhuman species', 'whether humans should make efforts to prevent the extinction of living species']