Americans love sports . But this hobby sometimes has serious results—at least to the players. For example, when people play tennis, sometimes they hurt their elbow（肘部）. Also it is easy to hurt a knee in a football game. These injuries（毁伤）happen while the player is having fun, but they still hurt.
   A few months ago, Kathleen Simmons, who loves playing volleyball, hurt her knee in a volleyball game. Her doctor told her that she needed a very difficult operation（手术）or she might not be able to play again. She felt very sad
   Then Simmons learned about “video operation”. With the help of this new science in medicine, doctors can now repair many injuries.
For this operation, her doctor didn’t have to open her knee. Instead he put a very small camera lens（镜头）inside her knee. The lens sent back pictures, which appeared on a television screen. As he worked, he could see the inside of her knee on the TV. With the help of the large pictures on the screen, the doctor knew exactly what to do when he was making the repairs.
   Simmons started walking five days after her operation. “My knee hurt a lot the first few days,” she said. “But I felt better very quickly.” Now, six months after her operation, Simmons can do everything she did before her injury. “It feels like a new knee,” she said. “I can even play volleyball again.”

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    河流①大小都是由一定区域范围内的雨水及地下水溢流汇聚而成。②那些空间污染特别严重的地区，天上降落的雨水原本③干净的；落到地面后，④地面污浊，雨水就会带着污染物渗入地下，汇入河流，形成我们常说的面源污染。⑤居民的生活污水、工厂和医院的废水⑥是点源污染的主要来源。