You are making a big mistake.

你正在犯一个严重的错误。

《牛津词典》

It was a big mistake on my part to have trusted her.

我相信了她，这是我的一大错误。

《牛津词典》

You are making a big mistake, Pinocchio.

你犯了个大错误，皮诺乔。

youdao

A year ago,he was campaigning for the presidency on the presumption that Iraq was a big mistake and we needed to focus on Afghanistan.

VOA: standard.2009.09.22

Maybe I made a big mistake by likening it to an organic chemistry course-- I don't mean to turn you off.

也许将其比作有机化学课,是个错误,我不是故意想倒你们胃口的

耶鲁公开课 - 金融市场课程节选

That's the big negativity in United States. The United States is making a huge mistake

这恰恰是美国的消极面了。美国正在犯一个大错误。

美国偶像 - SpeakingMax英语口语达人

And I think those who dismiss that out of hand make a big mistake.

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He said those who "don't propose to take action now" were "making a very big mistake".

BBC: Brown rejects June election talk

Have you ever made a big mistake, and if so, what did you learn about it?

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