名词
中文翻译：二级邮件
同义词：
['second-class mail', 'second-class postal service']
例句：
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1.The package arrived in a week, which is faster than the standard delivery time.
这个包裹一周就到了，比标准送货时间要快。
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2. The company offers a discount for customers who use their second-class mail service.
该公司为使用其二等邮件服务的客户提供折扣。
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3. I sent my parents a letter by second-class mail to save on postage costs.
我通过二等邮件给父母寄了一封信，以节省邮资费用。