老师请问B选项为何不对？

NO.PZ2021120102000028 问题如下 Whiof the following statements best scribes a cret curveroll-wn strategy? A.Returns from a cret curve roll-wn strategy cestimatebycombining the incrementcoupon from a longer maturity corporate bonwith priappreciation e to the passage of time. B.A synthetic cret curve roll-wn strategy involves purchasing protection using a single-name C contrafor a longer maturity. C.A cret curve roll-wn strategy is expecteto generate a positive return if the cret sprecurve is upwarsloping. C is correct. A cret curve roll-wn strategy willgenerate positive return only unr upwarsloping cret sprecurve. for thebenchmark yielchanges must separatefromchanges e to cret sprea, anunr asynthetic cret roll-wn strategy involves selling protection using asingle-name C contrafor 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 C 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，谢谢

NO.PZ2021120102000028 问题如下 Whiof the following statements best scribes a cret curveroll-wn strategy? A.Returns from a cret curve roll-wn strategy cestimatebycombining the incrementcoupon from a longer maturity corporate bonwith priappreciation e to the passage of time. B.A synthetic cret curve roll-wn strategy involves purchasing protection using a single-name C contrafor a longer maturity. C.A cret curve roll-wn strategy is expecteto generate a positive return if the cret sprecurve is upwarsloping. C is correct. A cret curve roll-wn strategy willgenerate positive return only unr upwarsloping cret sprecurve. for thebenchmark yielchanges must separatefromchanges e to cret sprea, anunr asynthetic cret roll-wn strategy involves selling protection using asingle-name C contrafor a longer maturity. 可以讲解下为什么c正确吗

NO.PZ2021120102000028 问题如下 Whiof the following statements best scribes a cret curveroll-wn strategy? A.Returns from a cret curve roll-wn strategy cestimatebycombining the incrementcoupon from a longer maturity corporate bonwith priappreciation e to the passage of time. B.A synthetic cret curve roll-wn strategy involves purchasing protection using a single-name C contrafor a longer maturity. C.A cret curve roll-wn strategy is expecteto generate a positive return if the cret sprecurve is upwarsloping. C is correct. A cret curve roll-wn strategy willgenerate positive return only unr upwarsloping cret sprecurve. for thebenchmark yielchanges must separatefromchanges e to cret sprea, anunr asynthetic cret roll-wn strategy involves selling protection using asingle-name C contrafor a longer maturity. 所以，A句话的表述是有问题的，正确的表示是加上assuming flbenchmark yielcurve这句话。还是没搞清楚怎么判断收益曲线stablestable曲线不变吧？是指上倾还是水平？什么时候曲线stable时指的是曲线水平flat？ 收益曲线不变代表ration不变吗？可否请老师详细一下

NO.PZ2021120102000028 问题如下 Whiof the following statements best scribes a cret curveroll-wn strategy? A.Returns from a cret curve roll-wn strategy cestimatebycombining the incrementcoupon from a longer maturity corporate bonwith priappreciation e to the passage of time. B.A synthetic cret curve roll-wn strategy involves purchasing protection using a single-name C contrafor a longer maturity. C.A cret curve roll-wn strategy is expecteto generate a positive return if the cret sprecurve is upwarsloping. C is correct. A cret curve roll-wn strategy willgenerate positive return only unr upwarsloping cret sprecurve. for thebenchmark yielchanges must separatefromchanges e to cret sprea, anunr asynthetic cret roll-wn strategy involves selling protection using asingle-name C contrafor a longer maturity. 如题

NO.PZ2021120102000028问题如下 Whiof the following statements best scribes a cret curveroll-wn strategy? A.Returns from a cret curve roll-wn strategy cestimatebycombining the incrementcoupon from a longer maturity corporate bonwith priappreciation e to the passage of time.B.A synthetic cret curve roll-wn strategy involves purchasing protection using a single-name C contrafor a longer maturity.C.A cret curve roll-wn strategy is expecteto generate a positive return if the cret sprecurve is upwarsloping. C is correct. A cret curve roll-wn strategy willgenerate positive return only unr upwarsloping cret sprecurve. for thebenchmark yielchanges must separatefromchanges e to cret sprea, anunr asynthetic cret roll-wn strategy involves selling protection using asingle-name C contrafor a longer maturity. whis synthetic roll wn strategy? how to use C