That was kind of a riskless trade because if they filed on time, we hadn't paid anything.

这是一种冒险的交易,因为如果他们按时发布，我们没有损失。

耶鲁公开课 - 金融市场课程节选

They kept a copy of that and they filed it away, so the government had a complete record of your payments into the system.

邮局留下存根并且归档保存，这样政府就能完整的记录下,你的支付情况。

耶鲁公开课 - 金融市场课程节选