Eyespots, the most rudimentary eyes, are found in protozoan原生动物 flagellates 鞭毛虫 , flatworms 扁形虫 , and segmented worms片段 蠕虫 .
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When carbon is added to iron in the proper proportions , the result is steel.
The first important exposition in the United States was held in Philadelphia in 1876.
Insect pests are among the leading causes of crop failure.
People who do not sleep enough tend to become irritable .