“Let’s challenge our states to adopt world-class standards,” he said, putting his finger on a huge problem.

“我们要挑战各州（现状），采用世界级的标准，”奥巴马的这句话准确的指出了一个（教育）大弊端。

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The second class of problem comes from the world of combinatorics.

第二类问题来自组合数学界。

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Class size is the problem the academic world pay attention to in the recent years and large-size class which breaks through the class-size limitation has problems.

班级规模是近些年学界比较关注的问题，而突破班级规模限制的大班教学存在许多问题。

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"If you throw municipal bonds into disorder, you're going to have a real world-class problem, " Ross was quoted as saying at a luncheon in New York.

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The first is a developed world problem, the challenge working-class youth without higher education face finding work in a de-industrialized society.

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The paperback is being made temporarily available at deep discount to support a world class charity, Charitywater, which quietly is solving a problem that kills more people than all forms of violence, including war: the lack of clean and safe drinking water.

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