阅读短文，选择正确的答案。

    Mrs. Jones was a teacher. Her house was not far from her school, and she often walked there in the morning. All the students in the school were very young.

    One cold and windy morning in October, Mrs.Jones walked to school. The cold wind went into her eyes and big tears（泪）began to run out of them. She reached (到达) the school, opened the door and went into the classroom.

    It was nice and warm there and Mrs. Jones was happy. But then a small boy looked at her for a while, put his arms a round her and said (说):"Don't cry, Mrs. Jones. School isn't very bad. "

用火柴棒按如图所示的方式摆图形，按照这样的规律继续摆下去，第n个图形需要____根火柴棒（用含n的代数式表示）．

席____    降____    欢____    路____    单____

钱____    孤____    颜____    粽____    原____