我确信他们讲的是真话。

I'm satisfied that they are telling the truth.

《牛津词典》

我确信你错了，凯特不像那样。

I'm sure you've got it wrong. Kate isn't like that.

《柯林斯英汉双解大词典》

我确信自己是正确的。

I'd convinced myself (that) I was right.

《牛津词典》

I'm sure there's some upper limit as there are to most things, like if we think of wavelengths and different types of light, there is so large that you can get, but you would be approaching that level.

我确信对于大多数事物,都会有一个上限，就像我们考虑波长和不同的光时，那个太大了，但是你可以接近那个量级。

麻省理工公开课 - 化学原理课程节选

But in the United States, I would say, most definitely, my favorite city, my favorite place I've ever been.

但我十分确信，在美国，在我去过的城市和地方中，我最喜欢纽约。

纽约的人们 - SpeakingMax英语口语达人

I am certain we would know that George Washington was the commander of our forces in our battle.

我十分确信你们都知道,乔治·华盛顿是战时美国军队的指挥官

耶鲁公开课 - 古希腊历史简介课程节选