I'm sorry, but I must go now.

对不起，但是我得马上走。

《柯林斯英汉双解大词典》

But I must warn you.

但是我必须警告你。

youdao

The little peasant said, "Oh, but I must have my beast back again."

小农夫说：“噢，但是我必须把我的小牛找回来。”

youdao

"But I must go now.Thank you."

VOA: special.2010.05.15

I wish I had more time, but I must be going.
I wish I had more time, but I must be going.

I wish 课堂 - SpeakingMax英语口语达人

But even as black Baptist, I could have gone certain black Baptist and run out, because I must struggle against homophobia, and my profound love for gay brothers and lesbian sisters.

作为一个黑人浸信教徒，即使我去黑人浸信会，也会被赶走，因为我必须于恐同症作斗争，以及我对同性恋者们深深的爱。

普林斯顿公开课 - 人性课程节选

He is always sincerely apologetic but I must admit he has a good excuse.

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But I must admit: the lack of invasiveness makes it a lot less fun to use.

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But I must say that while strong opinions are rewarded on the Internet, so is thick skin.

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