translation.en: About six months later I figured out it must be hydrogen, until some scientist told me the unfortunate truth, which is, you actually use more clean electrons than the ones you get inside a car, if you use hydrogen.
translation.zh: 六个月以后，我觉得答案必定是氢气， 直到后来某科学家告诉我一个不幸的事实： 你其实用了 比你所得到的更多干净的电子， 如果在汽车里使用氢气的话。