Young people believe efforts to reduce pollution, poverty, and war are doomed to failure. This pessimism is probably harmful to humanity' s future, because people lose motivation to work for goals they think are unrealizable. We must do what we can to prevent this loss of motivation and ttherefore must enable our children to believe that better futures are possible. Which one of the following is an assumption on which the argument depends? ['Enabling people to believe that better futures are possible will help prevent the loss of motivation that results from pessimistic beliefs about the future.', 'If future generations believe that the future can be better, then pollution, poverty, and war will be eliminated.', "Motivating people to work to solve humanity's problems will enable them to believe that the future can be better and will cause them to be less pessimistic.", "The current prevalence of such problems as pollution and poverty stems from previous generations' inability to believe that futures can be better."]