名词
中文翻译：分级环
同义词：
['grade ring', 'graded ring']
例句：
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1.The graded ring on the door is a symbol of protection and security.
门上的分级环是保护和安全的象征。
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2.The graded ring on the door is a symbol of protection and security.
门上的分级环是保护和安全的象征。
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3. The graded ring on the door is a symbol of protection and security.
门上的分级环是保护和安全的象征。