Genetics is a science that had already caused and great changes in our lives. A.will cause B.caused C.was causing D.had caused 答案:A某汽车发动机的功率为29.4kW,以36kW/h的速度匀速行驶,行驶了200km时,消耗汽油50kg.其中汽油的热值为4.6×107J/kg.求:(1)汽车速度匀速行驶了200km所用时间是多少秒?(2)汽油完全燃烧放出的热量(3)发动机的效率.