Which of the following is the best description of the spread premium puzzle:

A、Thespreadpremiumpuzzlereferstoobserveddefaultratesbeingmuchlessthanimplieddefaultrates,leadingtolowercreditbondsbeingrelativelycheapwhencomparedtotheiractualdefaultprobabilities
B、Thespreadpremiumpuzzlereferstodollardenominatednon-USsovereignbondsbeingpricedaatsignificantdiscounttoothersimilarUSDdenominatedassets
C、ThespreadpremiumpuzzlereferstoAAAcorporatebondsbeingpricedatalmostthesamepricesasequivalenttreasurybondswithoutofferingthesameliquidityorguaranteeastreasurybonds
D、Thespreadpremiumpuzzlereferstothemoralhazardimplicitinthemonolineinsurancemarket