在昨日白宫举行的记者会上，奥巴马表示：“这是一场已持续一段时间的缓慢发酵的危机，不是什么新情况。”
"This is a slow-rolling crisis that has been going on for some time. This is not new, " he said at a White House press conference yesterday.
研究结果从机理上解释了养殖场粪污进行沼气发酵处理时，出现产气量下降甚至不产气的原因。
The results of research explained why gas yield decreased when the faeces of livestock farms was handled with for biogas fermentation.
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