名词
中文翻译：键石活塞环
同义词：
['keystone', 'piston ring例句：1. The keystone of the engine is the piston ring.（发动机的键石是活塞环。）']
例句：
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1. The keystone of the engine is the piston ring.
发动机的键石是活塞环。
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2.The piston ring is essential for maintaining the engine's efficiency.
活塞环对于保持发动机的效率至关重要。
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3. The piston ring is designed to prevent oil from leaking out of the engine.
活塞环的设计是为了防止机油从发动机中泄漏出来。