He could not understand how people paid for food and valuable things with paper! He was also puzzled by the black stones people used to burn to produce heat.
他不明白人们是怎么用纸来买食物和贵重物品的！他还对人们用来燃烧产生热量的黑色石头感到困惑。
2
He was also puzzled by the black stones people used to burn to produce heat.
他还对人们用来燃烧产生热量的黑色石头感到困惑。
3
Factories that burn coal still polluted the air with a lot of black smoke.