In the A, B, C, D and F grading system, the first four letters are typically considered passing grades.

在 A、B、C、D 和 F 评分体系中，前四个字母通常被认为是及格。

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There are a number of vitamins that are vital for good hair health, the main ones being vitamins C, D and E, and in a balanced diet all these vitamins should be readily available.

有许多对头发健康至关重要的维生素，主要有维生素C、D和E，而在平衡的饮食中所有这些维生素应该很容易获得。

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A: Scientists have identified five unique hepatitis viruses, identified by the letters a, b, c, d, and E. While all cause liver disease, they vary in important ways.

答：科学家们已经识别出五种截然不同的肝炎病毒并以甲、乙、丙、丁、戊型作为辨识。虽然它们都会引起肝病，但在重要方面又有所不同。

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