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平面镜、凹面镜、望远镜,在现在看来都是很平常的物品,但这些东西第一次被制造出来时,都是伟大的发明。这些镜子是在什么时候开始出现的呢?
Flat mirrors, concave mirrors, and telescopes are all very common items now, but these were the first great inventions ever made. When did these mirrors start to appear?