If your child regresses to babyish behaviour, all you know for certain is that the child is under stress.

如果你的孩子退步到幼稚的行为，你可以肯定的是孩子正处在压力之下。

《柯林斯英汉双解大词典》

I don't know for certain why Carl Dadisman, the owner, wouldn't stop Daddy from sitting down.

我不知道出于什么原因，卡尔·达迪斯曼——这家店的店主——并不阻止爸爸坐下。

youdao

But he added, he did not know for certain.

但是他补充说，他也不确定。

youdao

But we are not going to know for certain which approach makes sense until additional data is in."

VOA: standard.2010.07.16

We don't know for certain. But what might have happened to lead to the two different editions?

我们不能确切知道，但可能发生过什么,导致了这两个不同版本？

麻省理工公开课 - 媒体、教育、市场课程节选

I think maybe for, you know, certain, maybe sort of older ladies who have sort of big hats,

我想可能有个别年迈的女人会有那样的大帽子，

英国皇家赛马会 - SpeakingMax英语口语达人

To know for certain whether praying for romantic partners strengthened relationships, they needed to go further.

ECONOMIST: Praying for your partner stops you straying

Or to know for certain whether they can hang on to their beloved items.

FORBES: The Return of the Mummy

He added that the midwife concerned could not know for certain who she had visited without the diaries.

BBC: Poole hospital midwife patients' details lost in theft