欲配置PH=5的缓冲溶液，应选用下列（）共轭酸碱对。

A#A.NH2OH2+-NH2OH(NH2OH2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(NH2OH2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(NH2OH2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(NH2OH2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)