118. --- How do you _____ your spare time?

--- Travelling, fishing and surfing through the internet.

A. employ                    B. elect                        B. choose                            D. Cost

电阻R₁和R₂ 串联后的总电阻为100Ω，已知R₁ =40Ω，R₂ =________Ω；他们并联后的总电阻为________Ω。