关于x，y方程组$\left\{\begin{array}{c}{x}^2+2y^2=6\\ mx+y=3\end{array}\right.$有一组实数解，那么m的取值范围是（　　）

鉴别空气、氧气、二氧化碳三瓶气体．通常的做法是（  ）

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The future is coming! All over the world there are many new ideas(想法) for new places to live and work in. Some of them will be in the sea! They will be very big and lots of people will live and work in them. The Americans are planning to build a town called Atlantis City. It will be in the sea，about five miles away from the land. But the most exciting idea comes from Japan. It is called Acropolis. Acropolis will be a huge sea city, with parks, schools, a hospital and an airport. And it will move! It will travel slowly around the world. There are just two problems. Acropolis will cost (花费) a lot of money to make. And for people who get seasick, it won't be much fun.