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。
However, as the evidence began to accumulate, experts from the Zoo felt obliged to investigate,
可是,随着证据越来越多,动物园的专家们感到有必要进行一番调查,