Yes, I'm not sure how to describe that exactly.

是的，我不确定怎样能准确地描述。

耶鲁公开课 - 现代诗歌课程节选

you could leave your response to the invitation slightly open-ended by saying you're not sure.

你可以表示你不确定，开放性地回复这个邀请。

I don't know 课堂 - SpeakingMax英语口语达人

Metaphysically,I'm not sure whether that's a possibility or not.

形而上学地，我不确定这是否可能。

耶鲁公开课 - 死亡课程节选

Flexibly,here are the criteria.

不确定地说，选择标准是这样的。

耶鲁公开课 - 新约课程节选