R1和R2电阻并联，等效电阻R是（)。

A.A. R=R1+R2

B.B. R=R1×R2/(R1+R2)

C.C. R=R1+R2/R1×R2

A.R=（R1XR2）/（R1+R2）

B.R=（R1+R2）/R1XR2

C.R=R1+R2

D.R=1/R1+1/R2

A.R1+R2

B.1/R2

C.1/R1

D.R1R2/(R1+R2)

A.A. R=(RlXR2)/(Rl+R2)

B.B. R=(Rl+R2)/RlXR2

C.C. R=Rl+R2

D.D. R=1/Rl+1/R2

A.R=R1+R2

B.1/R=1/R1+1/R2

C.1/R=1/R1-1/R2

D.1/R=1/R1×1/R2

A.I1=2I2

B.U1=2U2

C.P1=2P2

D.总电阻R=3R2

A.2Ω

B.4Ω

C.6Ω

D.4/3Ω

A.R=R1+R2

B.R=R1×R2

C.R=R1-R2

D.R=R1÷R2

A.1

B.2

C.3

D.4