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A. into B. called C. it D. to test E. about |
It seems that everyone has seen plants growing, but have you ever thought where they get their food? In the seventeenth century, a European scientist Van Helmot asked this question. Like most people, he thought that plants must get their food from soil (土壤). However, Van Helmot decided the theory (理论) with experiments.
First, he dried some soil, put it a pot and weighed it. Next, he weighed a small tree, planted it in the pot and added rain water. Then, he watered regularly (定期地) with rain water.
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A. are produced B. that C. a lot of D. why E. wrong |
After five years, he removed the tree from the pot and weighted it again. He found that the tree had got weight. When he weighed the soil, however, it was almost exactly the same as it had been five years earlier. So Van Helmot drew the conclusion (结论) that the tree grew by drinking water. Although it turned out to be , he showed the importance of the use of scientific evidence (证据) to support ideas.
We now know plants and trees make their own food. Their leaves, when exposed(暴露) to the air and sun, are like factories that can change the energy from the sun into chemical energy. During this process (过程), oxygen (氧气) and sugar . The oxygen is released (释放) back into the air, and the sugar is used by the plant as food.
