“The credit cycle is expected to improve. For purposes of diversification, both collateralized debt obligations (CDOs) and their underlying corporate bonds should be included in the portfolio. AA rated CDOs currently offer significant relative value for long-term investors as the yield spread reflects a BB default rate expectation for the underlying collateral. Moreover, the value of the senior tranches should increase by more than the value of the mezzanine tranches since default correlations are expected to increase.”
老师，请问以上标红字体的具体意思吗？只知道其他两个错在哪里，不知道这个为什么对？
