问题如下：
Two of the structured financial instruments that Easton and Avelyn are considering for Dynamo’s portfolio are collateralized debt obligations (CDOs) and covered bonds. Easton and Avelyn make the following comments about the securities.
Easton: If the correlation of the expected defaults on the CDO collateral of the senior and subordinated traches is positive, the relative value of the equity tranche compared with the senior and mezzanine tranches will increase.
Avelyn: Replacing a portion of the corporate bonds with CDOs will provide meaningful diversification to the investment portfolio.
Avelyn: Investing in covered bonds will give us the yield increase we are seeking compared with investing in corporate bonds or asset-backed securities.
Which comment regarding CDOs and covered bonds is accurate?
选项：
A. Easton’s comment
B. Avelyn’s first comment
C. Avelyn’s second comment
解释：
A is correct.
CDOs typically include some form of subordination. With subordination, a CDO has more than one bond class or tranche, including senior bond classes, mezzanine bond classes (which have credit ratings between senior and subordinated bond classes), and subordinated bond classes (often referred to as residual or equity tranches). The correlation of expected defaults on a CDO’s collateral affects the relative value between the senior and subordinated tranches of the CDO. As correlations increase, the values of the equity tranches usually increase relative to the values of the senior and mezzanine tranches
请问老师选项b为什么错呢谢谢
