按图示的规律搭下去，则所用火柴棒数a_n 与所搭三角形的个数n之间的关系式可以是____．

根据材料内容，选择正确答案。

    Mr. Brown is an old man. Every morning he goes for a walk in the park. And he comes home at twelve thirty for his lunch in the middle of the day.

But today a car stopped at his house at twelve 0'clock. Two policemen helped him get out. One of them said to Mr. Brown's daughter, "He can't find his way home in the park and ask us to take him home in the car."

    The daughter thanked the policemen and they leave. Then she asked her father, "Dad, you go to the park every day. But today you can't find the way. What's wrong?" The old man smiled like a child and said, "I can find my way home. But I don't want to walk home."

如图为我国某地区农业生产景观图．根据图中信息判断，图示地区位于我国的（    ）

①坚持求真务实的工作作风

②建立全面的行政监督体系

③克服懒政怠政提高行政效率

④坚持正确的政绩观和价值观