When it comes to the letter grade on your test or homework, you might notice that there is no letter. Have you ever thought about why that is so?

当涉及到你的考试或家庭作业的字母分数时，你可能会注意到没有字母。你想过为什么会这样吗？

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The museum said that every possible test has been done on the painting and insisted that "no inscriptions, letter or numbers, were discovered during these tests.

博物院称已经对《蒙娜丽莎》进行了一切可能的测验，并称“在测验中没发现任何题字、书信和数字。”

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Smith & Nephew slid 1.6 percent to 675 pence after the company got a warning letter from the FDA saying it failed to properly test medical devices.

英国施乐辉公司股价下跌1.6%，至675便士，该公司收到了美国食品药品管理局的警告信，表示施乐辉公司没有通过医疗设备测试。

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The California case, a rare test of the national security letter statute, involves an unnamed phone company that has been fighting the letter since 2011.

WSJ: Judge Strikes Down Secretive Surveillance Law

And school-district officials in Oklahoma complained recently about how test scores are factored into controversial new letter grades assigned to schools.

WSJ: Seattle Teachers Protest Exams

Halliburton then conducted another test using a modified procedure, the letter said, and the result for the first time indicated the slurry design would be stable.

CNN: STORY HIGHLIGHTS