常温下,0.1mol/L的KH2PO4和0.1mol/L的K2HPO4溶液pH分别约为4和11.将等物质的量的KH2PO4和K2HPO4混合后溶于足量的水形成溶液,下列推测合理的是( )A.上述溶液的pH范围为4~7B.上述溶液中:c(K+)>c(H2PO4-)>c(HPO42-)>c(OH-)>c(H+)C.上述溶液中:c(K+):[c(H2PO4-)+c(HPO42-)]=3:2D.上述溶液中:c(K+)+c(H+)=c(H2PO4-)+c(HPO42-)+c(PO43-)+c(OH-)