碳的循环在学校教科书中已经讲过了。

The carbon cycle is the stuff of school books.

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但是这些是重要的概念，我们已经讲过了。

But these are the important concepts which we've just gone through.

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我已经跟他们讲过了。

I have told them.

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我们真希望他已经和我们讲过了。

We wished he had spoken to us.

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我们真希望他已经和我们讲过了。

We wished he had spoken to us.

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