Even if he bores you stiff, it is good manners not to let him know it.

即使他把你烦透了，出于礼貌你也不能让他看出来。

《柯林斯英汉双解大词典》

All I did was let him know his behavior was unacceptable.

我所做的只是让他知道他的行为是不可接受的。

youdao

Most of my questions to him were greeted with a friendly laugh, but I managed to let him know where my arm hurt.

我向他提出的大部分问题都得到了友好的一笑作为回应，但我还是设法让他知道了我的手臂哪里疼。

youdao

But, you know, this undergraduate's very eager to do it, let's let him have a try.

就不值得我再花时间,寻找是否有粒子。

麻省理工公开课 - 化学原理课程节选

If you agree with me, email, Facebook, or tweet Marc and let him know.

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They thought that he was wasting his time, and they let him know it.

NEWYORKER: Silence, Exile, Punning

Two days after Jonathan's death, his mother texted Brown to let him know she was praying for the football team.

CNN: Students dress like Superman to remember football player