名词
中文翻译：闰年
同义词：
['leap year', 'intercalary year']
例句：
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1. The calendar uses a system of leap years to keep track of the dates.
日历使用闰年系统来记录日期。
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2. The Gregorian calendar was introduced in 1582 and has been used ever since.
公历自1582年引入，一直被使用至今。
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3. The moon is said to have a cycle of about 29.5 days, which is why we use the term "lunar month" instead of "month."
据说月亮的周期大约是29.5天，这就是为什么我们用“月球月”而不是“月份”。