符号Kb(HS-)是下列哪个反应的质子转移平衡常数？

A.HS- OH-=S2- H2O

B.HS- H2O=S2- H3O

C.HS- H2O=H2S OH-

D.HS- H3O =H2S H2O

正确答案：HS- H2O=H2S OH-