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    Peter always doesn't know the way. His friends often laugh at him. They say he needs a map to find the bathroom in his own house. In his eyes, every street looks the same, and he doesn't know which way to go. Sometimes he has to take a taxi home because he can't remember the way to his house.

    Peter watches a lot of films and reads a lot of books about animals. Each bird knows which way is south. Bats (蝙蝠) can fly at night and find their way with their ears. He feels embarrassed (困窘的) because all these animals have a good sense of direction. He tries to find his way with the help of stars in the sky. There is a star called the North Star, and he knows how to find it.     Of course, Peter's friends are still laughing at him, because he can only see the North Star outside when it is sunny at night. He can't tell the directions in the daytime or when he is inside or when it is cloudy.

将一个重量为G的小球从空中某点静止释放，落在竖直放置的轻弹簧上，压缩到最低点后，再被弹起．在答题卡上画出小球在最低点时的受力示意图．

某同学在研究马铃薯块茎细胞呼吸方式时，设计了如下实验：

实验一：取新鲜马铃薯块茎，洗净、切成碎屑．向锥形瓶中分别加入适量的马铃薯块茎碎屑，安装成图甲装置．每隔一段时间，从分液漏斗向锥形瓶A中注入适量过氧化氢溶液．观察装置中溴麝香草酚蓝水溶液的颜色变化．

实验二：取新鲜马铃薯块茎，洗净、切成碎屑．向锥形瓶C中放入适量的马铃薯块茎碎屑，并向C瓶充入N2替代瓶中空气，安装成图乙装置，一段时间后，观察装置中溴麝香草酚蓝水溶液的颜色变化．

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