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下列哪些属于齿轮的基本要素（ ）
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[音频]Directions：Fill in the blanks with the exact words you have heard.Scientists have identified thousands of knownspecies around the world. And only a few of themhumans. Most ants live in the,or out in nature. There, they keep other creatures in check, distribute，and cleanand decaying materials from the ground. A very small percentage of ants doto humans. But those are incredibly challenging to control. They are small enough to easilyinside your house. Live in colonies that number in the tens of thousands to the hundreds of thousands, and reproduce quickly. That makes them good atin, and hard to kick out. Once theyin, thesestart affecting your home.、（CET 4: 2019.06(1)）
激光与普通光的区别？
光的特性
产生激光的必要条件
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