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阅读理解 The next time you get caught jumping on your bed you can tell your parents with a straight face that you are not playing, simply getting ready got a promising career in “Mattress Jumping”. Believe it or not, there are some people who actually get paid to do that! According to Reuben Reynoso, a professional mattress tester at San Francisco's McRoskey Mattress Factory that still makes every mattress by hand, it is real work and needs some training. For a start, it's not all about jumping to new heights or doing tricks like professional athletes, but rather about feeling each are在地球上各生态系统中，对维持生物圈碳氧平衡贡献最大的是（）A.森林生态系统B.草原生态系统C.海洋生态系统D.农田生态系统