问题如下：
Credit risk includes
选项：
A.the risk of default.
the risk of upgrades and downgrades.
credit spread risk.
All the above
解释：
D is correct. All the above
All of these are derived from the creditworthiness (or the perceived creditworthiness) of the borrower
第一章节的时候李老师说了一个干扰项：credit spread增加，pirce 下降是market risk，咋个这里会的credit risk 有包含了这个风险啊
