GbEng
那条河长300公里。 The river is 300 kilometers in length.
为了安全起见，在市内开车时速不要超过三十公里。 For safety's sake, don't drive more than 30 kilometers per hour in the city.
飞机以每小时900公里的速度飞行。 The airplane flies at 900 kilometers an hour.