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。
In their efforts to persuade us to buy this or that product, advertisers have made a close study of human nature and have classified all our little weaknesses.
做广告的人在力图劝说我们买下这种产品或那种产品之前,已经仔细地研究了人的本性,并把人的弱点进行了分类。