成龙在录制《开学第一课》时提起自己的奋斗历程：大家现在看我很风光，可我真是一步一步苦过来的。人这一辈子，想干成点事，都要勇于吃苦、敢于坚持，这是人生的必修课，我的格言是永不放弃。这一材料告诉我们（    ）

①失败和挫折是强者成功的垫脚石    ②人生与挫折同行，经历挫折就能成功

③战胜挫折需要顽强拼搏                 ④坚强的意志是战胜挫折、坚定人生目标的保障

DNA分子完全水解后，得到的化学物质是(     )

增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改仅限一词；

2）只允许修改10处，多者（从第11处起）不计分。

    My name is Li Hai. I come from an island to the south of China called Hainan Island. There is a good number of animals living on or around the island. We have monkey, deer, birds or varieties of fish. Hainan Island is a place to know about fish. My father is a fisherman with which I have been on many fishing trips. He makes a living by fish on the sea. He was taught my brother and me many about different kinds of fish, several of which only live in the sea around Hainan Island. My hometown is real a beautiful place. It attracts many tourists in world.

如图，某酒店大门的旋转门内部由三块宽为2米，高为3米的玻璃隔板组成，三块玻璃摆放时夹角相同．若入口处两根立柱之间的距离为2米，则两立柱底端中点到中央转轴底端的距离为（　　）