You mustn't tell him about it.

你绝对不要告诉他这件事。

You don't have to tell him about it.

你不必告诉他这件事。

You could tell him to turn down the TV.

你可以告诉他把电视音量调低。

They tell him what the criminal looks like.

他们告诉他罪犯的长相。

Yes. Could you just tell him to call me back?

可以。你能告诉他回个电话吗？

He asked me to tell him where the aquarium was.

他叫我告诉他水族馆在哪里。

Leave it another week, then tell him he'll have to decide.

把此事再放一周，到时告诉他必须做出决定。

Why don't you tell him to do something quiet when you're studying?

你为什么不告诉他在你学习时做些安静的事呢？

Tell him directly and honestly that you were talking without thinking.

直接诚实地告诉他你说话不经过思考。

Tell him to call me back.

告诉他给我回电话。