六、综合填空(共10空，计10分)
阅读短文，根据短文内容及首字母提示，在空白处填入一个适当的单词。
Every time we drive a car, we put our lives and the lives of others at risk. Selfdriving cars are designed to reduce those risks by letting technology control our vehicles. (1)A rates for selfdriving cars have been much (2)l than the rates for humandriven cars. Google's selfdriving car has had (3)o 13 collisions(碰撞) after traveling 1. 8 million miles.
