translation.en: A rating can range from a so-called AAA, which means it's a top-performing product, and it can go down to the level of the so-called BBB-, which means it's a fairly risky investment.
translation.zh: 评级范围包括 从最顶尖的AAA 到最差的垫底级别 也就是BBB- 也就是说这是一项非常冒险的投资