NO.PZ2021120102000028
问题如下：
Which of the following statements best describes a credit curve roll-down strategy?
选项：
A.Returns from a credit curve roll-down strategy can be estimated by
combining the incremental coupon from a longer maturity corporate bond with price appreciation due to the passage of time.
A synthetic credit curve roll-down strategy involves purchasing protection using a single-name CDS contract for a longer maturity.
A credit curve roll-down strategy is expected to generate a positive return if the credit spread curve is upward sloping.
解释：
C is correct. A credit curve roll-down strategy will generate positive return only under an upward-sloping credit spread curve.
As for A, the benchmark yield changes must be separated from changes due to credit spreads, and under B, a synthetic credit roll-down strategy involves selling protection using a single-name CDS contract for a longer maturity.
听视频，老师讲的是相当于买一个长期的债券，所以是sell CDS protection。
没想明白为什么是相当于买一个长期的债券？
请老师帮忙解释，谢谢
