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概括大意和完成句子(第23~30题，每题1分，共8分) 下面的短文后有2项测试任务：(1)第23~26题要求从所给的6个选项中为指定段落每段选择1个小标题;(2)第27~30题要求从所给的6个选项中为每个句子确定一个最佳选项。 Learn about Light 1 Ancient civilizations were amazed by the existence of light for thousands of years. The Greek philosophers believed that light was made up of countless, tiny particles that enter the human eye and create what we call vision. However, Empedocles and a Dutch scientist named Christian Huygens believed that light was like a wave. According to them, light spread out and travelled like a straight line. This theory was accepted during the 19th century. 2 ln 1905, Albert Einstein published a research paper in which he explained what is referred to as the photoelectric effect. This theory explains that particles make up light. The particles Einstein was referring to are weightless bundles(束)of electromagnetic(电磁)energy called photons(光子). Today, scientists agree that light has a dual(二重) natureit is part particle and part wave. It is a form of energy that allows us to see things around us. 3 Things that give off light are known as sources of light. During the day, the primary source of light is the sun. Other sources of light include stars, flames, flashlights, street lamps and glowing gases in glass tube. | 
