| 摘 要： | Imagine yourself as an astronaut flying high above the Earth.The most important thing in your spaceship is not your camera or your radio.The most important thing you have is your garden,where you grow food to eat and air to breathe.Growing air?Well,that isn't exactly what happens.But plants do take carbon dioxide from the air and use the light and water that help them grow to make oxygen.Take a deep breath. That came from a plant!It took 1.5 billion years of plants making oxygen before there was enough oxy- gen for us to breathe.
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