The cost of third-class mail has gone up by 50 per cent.

第三类邮件的邮资上涨了50%。

《柯林斯英汉双解大词典》

A domestic example is the post Office; private postal companies make a profit delivering third-class mail at half what the post Office charges to deliver it a loss.

举一个国内的例子是国家邮局；私人邮政企业对第三类的邮件的收费比国家邮局低一半，但仍可以从中盈利，而国家邮局却在赔钱。

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