听力原文： Why do we need a space station? Couldn't we do all those science experiments here on Earth. After all, the Space Station is expensive, and living in space can be dangerous. One of the answers has to do with gravity. Scientists learn about things by doing experiments. Imagine you are a scientist who wants to understand how sunlight affects plants. You would do an experiment by putting one plant in bright sunlight and another plant in a dark room. Then you would watch them over several weeks and see what happens to the plants. Or maybe you wonder how gravity affects plants. You would put oneplant in a room with normal gravity, and another in a room with no gravity. But wait a minute! There is no such thing as a no-gravity room on Earth. But the Space Station has them! Everything is weightless on the Space Station. That makes it a great laboratory for studying the effects of gravity. Scientists do the same experiments on the ground as on the Station. They know that any differences are caused by gravity. We already know that some chemicals combine differently in zero-gravity. Some physical things are different, too. Fires bum differently and fluids don't flow in the same way as on Earth. Even our bodies change without gravity. Station researchers can study many different areas, like biotechnology, biomedicine, fluid physics, and so on. They can make quite a list! (26)