单项选择题

A.P1-P2+101g(R2/R1)-6(dB)
B.P1-P2+101g(R1/R2)-6(dB)
C.P1-P2+1g(R2/R1)-6(dB)
D.P1-P2+0.51g(R2/R1)-6(dB)