Credit ratings range from a high AAA to a low d.

信用评级的范围从最高的AAA级到最低的D级。

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Standard & Poors uses a very similar system, starting at AAA and ending at D, which indicates an issue in distress.

标准普尔使用大致相同的系统，从AAA到最后表示债券出问题的D。 。

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And who'd be first in line for an AAA or a junk rating?

BBC: Rio: Rating the environmental stars

The agencies assess their the ability to pay off loans or investments and then rate them on a sliding scale, ranging from AAA to D.

CNN: Explainer: The power of credit rating agencies