I wouldn't have troubled him so much if I had known he was so busy.

如果我知道他这么忙，我就不会这么麻烦他了。

youdao

If I had known the exercises should be handed in today, I'd have finished them yesterday.

如果我知道今天要交练习题，我昨天就会把它们做完了。

youdao

If I had known my life was going to turn out like this, I would have let them kill me.

如果我知道我的一生会是这样的结果，我早就该让他们杀了我。

《柯林斯英汉双解大词典》

If I had known, we would have maybe rolled out a cake or something. (Laughter.) But have fun.

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If I had known the restaurant's name, I would have known it was closed for lunch on Mondays, when I went.

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If I had known the truth I could have done something about it, I could have got her into hospital earlier.

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