translation.en: So, once you have mobility, now you're making a lot of engines because you've got lots of units, as opposed to steam ships or big factories where you're not making as many units, so this was the engine that ended up benefiting from mass production where all the other engines didn't benefit.
translation.zh: 所以，你可以自由组合， 现在能够用大量的引擎组合单元， 蒸汽船或是大的工厂里却不能够使用如此多的单元， 内燃机利于量产化 而其他各类引擎都不具备此能力。