john wAgnEr's most EnDuring ContriBution to thE stuDy oF AFro-AmEriCAn poEtry is his insistEnCE thAt it ______ in A rEligious, As wEll As worlDly, FrAmE oF rEFErEnCE.
A．is to BE AnAlyzED
B．BE AnAlyzED
C．hAs BEEn AnAlyzED
D．shoulD hAvE BEEn AnAlyzED