问题如下：
In May of 2005, several large hedge funds had speculative positions in the collateralized debt obligations (CDOs) tranches. These hedge funds were forced into bankruptcy due to the lack of understanding of correlations across tranches. Which of the following statements best describes the positions held by hedge funds at this time and the role of changing correlations? Hedge funds held a:
选项：
A.long equity tranche and short mezzanine tranche when the correlations in both tranches decreased.
B.short equity tranche and long mezzanine tranche when the correlations in both tranches increased.
C.short senior tranche and long mezzanine tranche when the correlation in the mezzanine tranche increased.
D.long mezzanine tranche and short equity tranche when the correlation in the mezzanine tranche decreased.
解释：
D is correct. A number of large hedge funds were short on the CDO equity tranche and long on the CDO mezzanine tranche. Following the change in bond ratings for Ford and General Motors, the equity tranche spread increased dramatically. This caused losses on the short equity tranche position. At the same time, the correlation decreased for CDOs in the mezzanine tranche, Which led to losses in the mezzanine tranche.
李老师上课的时候不是说了这里其实是short equity tranche CDS?long mezzaine tranche CDS
因为出现financial crisis，CDS on equity tranche开始涨价，因为correlation上升
但是按理来说，难道灾难来临时，mezzanine的correlation为啥不上升
还是说只是根据图形（PPT），整个知识点感觉掌握的很模糊，能再讲一讲吗
