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为什么卡车和拖拉机需要那么大的车轮呢?因为大车轮可以帮助它们在打滑的路面增加摩擦力,在拉动重物时进退自如。
Why do trucks and tractors need that big wheel? Because large wheels can help them increase friction on slippery roads and move back and forth as they pull heavy loads.