My car’s performance is ___ since the engine’s been tuned and the tires have been changed．
A.better as twiceB.twice as the conditionC.twice as goodD.twice as better在线课程C
考查倍数问题。倍数 + as + 形容词，句意：这辆汽车调了发动机和换了轮胎以后性能好了一倍。选C。