Fifty-litre carboy would be the most economical size. Carboys may be retained without charge for two months.
50升的瓶子应是最经济的尺码,这些瓶子可免费保存两个月。
To get a full appreciation of what this means we must turn first to some recent human inventions.
要透彻理解这句话的意义,我们应先回顾一下人类最近的几项发明。