某个同学为探究鱼鳍在游泳中的作用，选取甲，乙，丙三条相同的鲫鱼，放于同一鱼缸中，操作步骤之一是只用纱布捆扎甲的胸鳍，其他鳍呈自然状态；操作步骤之二是只用纱布捆扎乙的尾鳍，其他鳍呈自然状态；丙不作处理。请问：
（1）上述探究设计包括 组对照实验。
（2）甲和丙，乙和丙的实验变量分别是 和
（3）探究实验结束后，各小组交流了实验结果，最后得出了以下结论：
鱼在游泳时，靠 鳍保持平衡，靠 鳍保持前进的方向。
（1）2
（2）有无胸鳍的作用 有无尾鳍的作用
（3）胸 尾
题目分析：甲丙、乙丙只有一个变量，分别构成对照，所以是两组对照实验，用纱布捆扎甲的胸鳍所以甲和丙实验变量是有无胸鳍的作用；用纱布捆扎乙的尾鳍乙和丙实验变量是有无尾鳍的作用，由变量所以推出结论鱼在游泳时，靠胸鳍保持平衡，靠尾鳍保持前进的方向
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| Lightning flashed through the darkness over Sibson's bedroom skylight (天窗). Sibson was shaken by a clap of thunder_1_ he knew what was happening. The storm had moved directly _2_ his two-story wooden house. Then he heard the smoke alarm beeping. Sibson rushed down the stairs barefoot to 3 ; he opened the door to the basement (地下室), and flames 4 out. Sibson ran back upstairs to call 911 from his bedroom. "I felt 5 because the room had a separate outdoor stairway," he explains. But the phone didn't work, and when he tried to go down the outdoor stairway, he was 6 by a wall of flames. Sibson realized he was trapped (困住). Sibson's house was three kilometers 7 the main road and was so well hidden by trees that he knew calling for help would be 8 . Up a hill nearby lived Sibson's neighbor, Huggons. He was lying in bed when something like a smoke alarm 9 his ears. He jumped out of bed, took his 10 and flashlight, and headed down the hillside toward the 11 . That was when he saw the rolling heavy smoke. Huggons dialed 911, and the operator warned him not to 12 the house. But Huggons said, "There is no way I am going to listen to Sibson 13 and die in that fire." "Anyone there?" Huggons called out. Then he heard "Help! I'm trapped!" coming from the second floor balcony (阳台). He entered the house, but soon had to run back to catch his 14 . After one more 15 inside the house, Huggons gave up and 16 around back. The wind parted the smoke just 17 for him to catch sight of Sibson. But there was no way to get to him. He 18 the flashlight into the woods and noticed a ladder. He took it over to the balcony and 19 Sibson down just as the second floor of the house fell off. Sibson is still 20 when he tells the story. " I was alone that night," he says. "Then I heard the most beautiful sound in my life. It was Huggons." | ||||
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