But he added, he did not know for certain.

但是他补充说，他也不确定。

youdao

Mr Suttles said he "did not know for certain" why it had failed.

Suttles先生说他“并不十分确定”前种方案失败的原因。

youdao

I do not know for certain what the future holds but I am confident that with hard work, a little bit of luck and a supportive network of friends, I can be as successful as I want to be.

我不确知未来，但我相信通过艰苦的工作加上一点点的运气和朋友们的帮助，我一定能够心想事成！

youdao

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

VOA: standard.2010.07.16

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

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Walgreen may not know for certain which plans are steering big orders to mail vendors, but says it will find out using internal sleuthing.

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While he conceded that the public could not know for certain whether the secrecy is due to phone intercept evidence, Mr Ryder called for an "urgent review" into the provision which prevents disclosure and discussion of telephone intercept evidence which he said was "exceptional".

BBC: 'I'd prefer to know the truth' of Duggan death