The night before a midterm exam, you decide to go to the movies instead of studying for the exam. You score 60 percent on your exam. If you had studied the night before, you'd have scored 70 percent. What was the opportunity cost of your evening at the movies? (在中期考试前一天晚上,你决定去看电影,而不是考试。你的考试成绩达到60%。如果你以前学习了一天,你就得到了70%的收视率。你晚上在电影中的机会成本是多少?——中文由在线翻译而来,仅供参考.下同.)