They all look so alike to me that I'm never sure which is which.

它们在我看来简直一模一样，我永远分不清哪个是哪个。

《柯林斯英汉双解大词典》

I'm never sure what I'm going to be, from one minute to another!

我永远也不知道下一分钟自己会变成什么样子！

youdao

And the force caused by the magnetic field, I am never sure about the sign.

由磁场生成的力，我不确定其符号。

youdao

Ethan Holtzman says his band attempts to shine a light on this fact to help make sure such a situation never happens again.

VOA: special.2011.05.06

How can individuals who are biologically autonomous, who judge and see matters very differently from one another, who can never be sure whether they trust one another, ? how can such individuals accept a common authority?

在生理上独立的个人，可以从不同角度,判断和看待事物的个人，永远不可能知道他们是否能互相信任的个人，这些个体如何才能接受一个相同的权力制约呢？

耶鲁公开课 - 政治哲学导论课程节选

Then he stopped. He said: "I never,in all my life, felt more sure that I was doing right than I do in signing this paper.

VOA: special.2009.10.08

Woods never liked that question, perhaps because he's never sure how far he's going.

NPR: A Long Road Back To No. 1 For Tiger Woods

He shared with me always, though I was never sure what I brought to our partnership.

NPR: Eggers Blends Fact, Fiction of Sudanese 'Lost Boys'

Volunteers are never sure of the conditions they might face when deployed to disaster sites or developing countries.

CNN: 'Geocoding' used to locate Katrina survivors