Since that is not so, I suppose I must do it.

既然不是这样，我想我必须这样做。

youdao

I think we must do something to protect the environment.

我认为我们必须做些什么来保护环境。

youdao

I also think we must do something about the insanity plea.

我还认为我们必须对疯狂的抗辩采取行动。

youdao

But what I do remember was, at the end of that long, continuous coverage it must have been about two a.m.

VOA: special.2009.08.16

He says, "I believe in the practice and philosophy of what we have agreed to call magic, in what I must call the evocation of spirits, though I do not know what they are."

他说我相信我们所称作的,关于魔法的实践和哲学，我认为那是对灵魂的召唤，尽管我并不知道它们是什么“

耶鲁公开课 - 现代诗歌课程节选

When you say "I must" what you mean is "I need to do something."

当你说 "I must"的时候，你是指“我必须得做某事。”

Must 课堂 - SpeakingMax英语口语达人

First of all I must confess, I do trade.

FORBES: The Great Apple Trade?

Question: Why must I do the job at all?

FORBES: Digital Rules

"I must say that what I do, and I don't mean to sound arrogant about this, but what I do, I think I'm the best at it, " Rose said.

WSJ: Pete Rose Works Full-Time Selling His Signature in Las Vegas