Bethany: Psychologists have discovered a technique for replacing one' s nightmares with pleasant dreams, and have successfully taught it to adults suffering from chronic nightmares. Studies have found that nightmare-prone children are especially likely to suffer from nightmares as adults. Thus, psychologists should direct efforts toward identifying nightmare-prone children so that these children can be taught the technique for replacing their nightmares with pleasant dreams. Which one of the following principles, if valid, most helps to justify drawing the conclusion in Bethany's argument? ['Any psychological technique that can be successfully taught to a child can also be successfully taught to an adult.', 'Psychologists should do everything they can to minimize the number of adults troubled by chronic nightmares.', 'Psychologists should not teach the technique for replacing nightmares with pleasant dreams to children who are unlikely to suffer from nightmares as adults.', 'Identifying nightmare-prone children is generally more difficult than teaching adults the technique for replacing nightmares with pleasant dreams.']