材料一：明代长城东起鸭绿江边，西至甘肃省嘉峪关，全长6 000多千米，是中国古代最宏伟的军事防御工程。万里长城被视为中华民族的象征和骄傲。

材料二：相传2 000多年前，秦始皇修长城时，强征天下民夫。孟姜女的丈夫也被抓去，累死在长城脚下。孟姜女千里寻夫送寒衣，得到的却是丈夫的死讯，她悲恸欲绝，竟哭倒了长城。

材料三：见下图。

阅读理解

Found

A set of keys. There is a toy bear on it, too.  If you lose it, call me at 880-1167313.  I'm from No. 2 Middle School.

                                                                                            Jack  Lost

An old bike.  It's black with a plastic(塑料的)basket.  Its seat is yellow.  If you find it, please return it to me.  I live in the fifth floor in Building 2.

    Miller   Lost

Yesterday, I lost a novel written by Mo Yan.  Its name is Frog.  I’m eager(渴望的)to find it.  If you find it somewhere, can you return it to me? I’m from Class 6, Grade 7.

                                               Louis

下列函数①y=2x﹣1，②y=πx，③y=$\frac{3}{x}$，④y=x²中，一次函数的个数是（　　）

如图，菱形ABCD的边长为2，$\angle A={60}^{°}$,M为DC的中点，若N为菱形内任意一点（含边界），则$\overrightarrow{AM}·\overrightarrow{AN}$的最大值为（   ）