阅读下列材料：

材料一 圣贤的经训格言，断断不是万世不变的法则……冲破过去历史的网罗，创造民主的“青春中国”。——李大钊

材料二只有这两位先生(指民主和科学)，可以救治中国政治上、道德上、学术上、思想上一切的黑暗。若是因为拥护这两位先生，一切政府的压迫，社会的攻击笑骂．就是断头流血。都不推辞。——陈独秀

材料三 中国人民在思想上迷信、盲从的“病”，必须用“科学”这味药来诊治。——鲁迅
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阅读短文，下列问题

People sometimes like to read stories of dogs very much. They think that dogs are much cleverer than cats, sheep, cows or other animals in their homes.

One of my close friends, Bob, has a very large police dog named Jack. Every Sunday afternoon, Bob and Jack have a walk in the park nearby. Jack likes these walks very much. One Sunday afternoon, I paid a visit to my friend. I stayed there for a long time and my friend and I had much more talk with each other than ever before. Soon it was time for them to take a walk in the park. We forgot that. Jack became worried about it. He walked around the room several times and then sat down in front of me and looked at me. But I still paid no attention (注意) to him. I went on talking with my friend. At last, Jack could not wait any longer. He went out of the room and came back a few minutes later. He sat down in front of me again. But this time, he held my hat in his mouth. Suddenly, I understood what Jack meant and so did my friend.

据报道，中国首艘001A型17号国产航母于2017年4月23日前后下水并进行相关测试。从外观上来看该国产航母与16号辽宁舰大致相同，也是常规动力航母，最少可以搭载36架歼-15舰载机。它的满载排水量80000吨，此时的吃水深度为12m。 为了方便计算，ρ_海=1.0×10³kg/m³，g=10N/kg，求：