I would normally suggest taking time off work, but in this instance I'm not sure that would do any good.

我通常会建议休假，但就这个情况而言，我不敢保证休假会有什么好处。

《牛津词典》

I'm not sure that this is the most valuable use of my time.

我不能肯定我的时间这样来安排最有价值。

《牛津词典》

I'm not sure that I understand. Go over it again.

我不敢说我搞懂了。请再来一遍吧。

《牛津词典》

"Celebrating with our family." "Presents!" "I usually get presents that say Santa Claus on them but I'm not really sure if they're from him."

VOA: special.2009.12.21

I'm not at all sure there's anything more to be said about that passage, which I think lays it to rest.

我不确定这篇文章是不是,还要更多的讲解，就这样的吧。

耶鲁公开课 - 文学理论导论课程节选

I'm not sure there might be additional things that international students have to do like additional tests.

我不确定留学生录取是不是还有其他要求，比如说还要加试什么的。

被学问的自由所迷住 - SpeakingMax英语口语达人

I'm sure there are some folks in the financial service industry who make that argument, although I'm not sure that they make it with a straight face.

WHITEHOUSE: President Obama Speaks on Confirming Richard Cordray

First of all, I would say that it's based on anonymous sources, so I'm not sure that it's true, and hopefully it's not because it reports that Speaker of the House John Boehner, in a closed meeting with House Republicans, called the discussion over whether or not to allow student interest loan rates to double a phony debate.

WHITEHOUSE: Press Briefing

But beyond that, I'm not sure that the announcement today goes particularly to your question.

WHITEHOUSE: Press Briefing