单项选择题

A.Pt ∣ H2(PH2 = Pθ)∣OH-(a=1)
B.Pt ∣ H2(PH2=Pθ)∣H+(a=1)
C.Pt ∣ H2(PH2=Pθ)∣H+(a=10-7
D.Pt ∣ H2(PH2=Pθ)∣OH+(a=10-7