Ja bym zostawił nazwę własną, a w nawiasie podał objaśnienie.

The GED is sometimes referred to as a "General Equivalency Diploma" or "General Education(al) Diploma." These and other improper references to the "GED" trademark are not authorized by the American Council on Education, which develops the tests and sets the rules for their use. Jurisdictions award a "Certificate of General Educational Development" or similarly titled credential to persons who meet the passing score requirements


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eksternistyczny dyplom ukończenia szkoły średniej

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Zaoczna matura

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Note added at 2 hrs (2008-01-24 13:30:24 GMT)
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The Tests of General Educational Development, or GED Tests, are a battery of five tests which, when passed, certify that the taker has American or Canadian high school-level academic skills. To pass the GED Tests and earn a GED credential, test takers must score higher than 40 percent of graduating high school seniors nationwide. Some jurisdictions require that students pass additional tests, such as an English proficiency exam or civics test

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Note added at 3 hrs (2008-01-24 13:34:05 GMT)
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Tzn. podałbym tłumaczenie, a w nawiasie zamieściłbym skrót (GED).