So, in terms of practicing this weekend, I mentioned that instead of getting a problem-set today, what I am going to be posting is optional extra problems.

而对于这周的练习，我曾经说过今天将不会布置作业，但是会布置一些额外的习题。

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Well, this whole business presents the problem I mentioned a moment ago.

这所有的内容都契合了,我刚才提到的问题

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President Obama has mentioned correcting this problem on several occasions, but still no significant action has been taken.

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This is a problem because as mentioned earlier, the energy producers are vanishing, and with their disappearance, so is supply.

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This problem was noted by the above-mentioned Tom Knutson.

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