Cho sơ đồ chuyển hóa : 

Câu hỏi: Cho sơ đồ chuyển hóa : ${\mathrm{P}}_2{\mathrm{O}}_5\stackrel{+\mathrm{KOH}}{\to }\mathrm{X}\stackrel{+{\mathrm{H}}_2{\mathrm{PO}}_4}{\to }\mathrm{Y}\stackrel{+\mathrm{KOH}}{\to }\mathrm{Z}$

A. ${\mathrm{K}}_3{\mathrm{PO}}_4, {\mathrm{K}}_2{\mathrm{HPO}}_4, {\mathrm{KH}}_2{\mathrm{PO}}_4$

B. ${\mathrm{KH}}_2{\mathrm{PO}}_4, {\mathrm{K}}_2{\mathrm{HPO}}_4, {\mathrm{K}}_3{\mathrm{PO}}_4$

C. ${\mathrm{K}}_3{\mathrm{PO}}_4, {\mathrm{KH}}_2{\mathrm{PO}}_4, {\mathrm{K}}_2{\mathrm{HPO}}_4$

D. ${\mathrm{KH}}_2{\mathrm{PO}}_4, {\mathrm{K}}_3{\mathrm{PO}}_4, {\mathrm{K}}_2{\mathrm{HPO}}_4$