如果他忘记支付租金，他的房东会给他发一个提醒。

If he forgot to pay his rent, his landlady would send him a ___reminder.

“时间宝贵”是对我们职责的持续提醒。

"Time is precious" is a constant ___reminder of our duties.

那封旧信是他们友谊的一个提醒。

The old letter served as a ___reminder of their friendship.