求翻译：教练车在接近于中等车速时燃油耗量最低，高速时随车速增加而迅速增加。这是因为在高速行驶时，教练车的行驶阻力增大所致；而低速时，由于发动机的负荷率低而导致油耗量增大。是什么意思？

Coach car lowest fuel consumption at close to medium speed, high speed with the speed increase is increasing rapidly. This is because when running at high speed, resistance due to the increase of the coach cars and low speeds, fuel consumption due to engine load rate of low volume increases.