欲配制pH=5的缓冲溶液，应选用下列（）共轭酸碱对。

A#A.NH2OH2+—NH2OH(NH2OH的pKb=3.38)#B.HAc—Ac-(HAc的pKa=4.74)#C.NH4+—NH3?H2O(NH3?H2O的pKb=4.74)#D.HCOOH—HCOO-(HCOOH的pKa=3.74)

B#A.NH2OH2+—NH2OH(NH2OH的pKb=3.38)#B.HAc—Ac-(HAc的pKa=4.74)#C.NH4+—NH3?H2O(NH3?H2O的pKb=4.74)#D.HCOOH—HCOO-(HCOOH的pKa=3.74)

C#A.NH2OH2+—NH2OH(NH2OH的pKb=3.38)#B.HAc—Ac-(HAc的pKa=4.74)#C.NH4+—NH3?H2O(NH3?H2O的pKb=4.74)#D.HCOOH—HCOO-(HCOOH的pKa=3.74)

D#A.NH2OH2+—NH2OH(NH2OH的pKb=3.38)#B.HAc—Ac-(HAc的pKa=4.74)#C.NH4+—NH3?H2O(NH3?H2O的pKb=4.74)#D.HCOOH—HCOO-(HCOOH的pKa=3.74)