What does the "tragedy of the commons" refer to? a. the idea that countries must limit the amount of immigrants they allow in order to preserve resources for their children b. the idea that one person who takes more than his or her share in a system of voluntary restraint will ruin the entire system c. the idea that those in a lifeboat who feel guilty about being safe should give up their space to someone in the water d. the idea that countries constantly given handouts will never learn to properly manage their own resources