名词
中文翻译：第一无穷序数同义词
同义词：
['first', 'primary', 'first-class']
例句：
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1. This is the first time I have visited this city.
这是我第一次访问这座城市。
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2. The first-class service makes our customers happy.
一流的服务让客户满意。
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3. In mathematics, the first-class set is a subset of the second-class set.
在数学中，第一类集合是第二类集合的子集。