A.dUMP B.TMP C.UDP D.UMP E.dCMP
A.AlA B.Asp C.Gln D.Glu E.Gly
A.N5CH-NH-FH4 B.N5-CH3-FH4 C.N10-CHO-FH4 D.N5,N10-CH2-FH4 E.N5,N10=CH-FH4