题目

阅读下面短文，根据所给情节进行续写，使之构成一个完整的故事。Carterenjoyed riding the school bus home. The ride home gave him some time to relaxafter a busy day of fifth grade. He usually sat alone and enjoyed that too.With four siblings(兄妹) he didn't get muchtime alone. Sometimes he sat with his younger brother, Jackson, butJackson was sick at home today.Thebus stopped and the tallest boy in his class, Dexter, stepped offfollowed by his younger brother, Billy. As the bus pulled away, Carterlooked back over his shoulder to watch the boys. Dexter was yelling and从集合{O，P，Q，R，S}与{0，1，2，3，4，5，6，7，8，9}中各任取2个元素排成一排（字母和数字均不能重复）．每排中字母O，Q和数字0至多只能出现一个的不同排法种数是______．（用数字作答）．