Two men are walking in the park. One is Mr. Brown, a worker, the other is Mr. Black. Mr. Brown is going to a chair. It is next to the road. Mr. Black is after him. Mr. Brown finds Mr. Black. Now Mr. Black begins to walk faster (更快). Because he wants to get to the chair before Mr. Black. Now Mr. Black begins to walk faster because he also wants to get to the chair first. Then they both run. Mr. Black runs faster than (比) Mr. Brown. So he gets to the chair first and sits down on it. Mr. Brown runs after Mr. Black. When he gets to the chair. He sees Mr. Black sitting on it. He is sorry to show a notice(通知)with the words“Wet Paint(油漆未干)”to Mr. Black. Now Mr. Black knows why Mr. Brown is going to the chair.

如今，对于大多数人来说，拍下一张照片是最容易不过的事。照片在我们的生活中随处可见，自拍照、毕业照、旅游照、新闻照等，比比皆是。照片记录了生活点滴。照片呈现了大千世界，有的令人喜悦、感动，有的令人痛苦、惭愧，有的令人思索、回味……总有那么一张照片会让我们印象深刻。

请以“总会想起那张照片”为题，写一篇文章。

要求：①文体自选（诗歌除外）；②不少于500字。

    三年以来，在人民解放战争和人民革命中牺牲的人民英雄们永垂不朽!

    三十年以来，在人民解放战争和人民革命中牺牲的人民英雄们永垂不朽!

    由此上溯到一千八百四十年，从那时起，为了反对内外敌人，争取民族独立和人民自由幸福，在历次斗争中牺牲的人民英雄们永垂不朽!

请回答：

在“验证机械能守恒定律”的实验中，实验装置如图甲所示．