问题如下：
Which of the following statements regarding commercial mortgage-backed security (CMBS) is correct?
选项：
A.Call protection will improve the credit rating of CMBS.
B.Some CMBS are recourse loan.
C.Balloon payment in CMBS is credit positive for investor.
解释：
A is correct.
CMBS are no recourse loans. Balloon payment increased extension risk for investor, which is credit negative.
有道类似的题问哪个可以增加信用评级的，选的是 subordinate，因为是内部信用增级的方式，那个题里也有 call protection，结果没有选，我就以为call protection没有improve the credit rating 的功能，结果到这个题目里，反而有improve the credit rating 的能力了？
