问题如下：
Zhang is a credit analyst in a securities company. For the CDOs and covered bonds, Zhang made the following statements?
Statement 1: Because covered bonds provide dual protection for creditors, they usually carry lower credit risks and offer lower yields.
Statement 2: Compared with investment in corporate bonds, CDOs do not offer unique exposure to a sector or market factor.
Statement 3: Mezzanine and equity tranches of CDOs provide a mechanism for investors to gain additional return if the underlying collateral has strong returns.
According to the information above, which of the following is correct?
选项：
A. Statement 1 and Statement 2 are correct
B. Statement 2 and Statement 3 are correct
C. All the statement are correct
解释：
C is correct.
考点：Structured Financial Instruments概念理解
解析：三个Statements都是正确的，为原版书和讲义给出的结论。
statement 2 怎么理解？为什么是对的？