问题如下：
Which of the following statements is correct regarding spread measures?
选项： The yield spread and i-spread are
equal if the benchmark yield curve is flat.
The z-spread = OAS for callable bonds.
C.The z-spread must be used for mortgage-backed securities (MBS).
D.The CDS spread is used only with corporate bonds.
解释：
A If the yield curve is flat, there is no need for interpolation. Therefore, yield spread = i-spread. z-spread > OAS for callable bonds. OAS must be used for MBS. CDS measures the credit risk from any security with positive probability of default including sovereign and municipal bonds.
这些spread是在ppt
那一页讲的？
