已知R1=3Ω，R串=9Ω；∵R串=R1+R2∴R2=R串-R1=9Ω-3Ω=6Ω；又∵ 1 R并 = 1 R1 + 1 R2 ∴R并= R1R2 R1+R2 = 3Ω×6Ω 3Ω+6Ω =2Ω．故选C．
