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    Tom, Sam, Jim and Jack live in a building of four floors. They live on different floors. They have different jobs―an engineer, a worker, a teacher and a doctor. Tom lives above Sam, but below(在下面) Jim. Jack lives on the third floor. The doctor lives above the teacher, but below the worker. The engineer lives on the ground floor. What are their jobs? Which floor does each of them live on?

将等质量的甲、乙两金属分别与足量的稀硫酸反应，产生氢气的质量与反应时间的关系如图。关于甲、乙两金属判断合理的是（ ）

用蘸有浓氨水的玻璃棒靠近下列各浓酸时，均有白烟产生的一组是（　　）

计算$4\sqrt{\frac{1}{2}}+3\sqrt{\frac{1}{3}}-\sqrt{8}$的结果是