The first is that expensive oil and relentless competition among airlines have put greater pressure than ever on aircraft and jet-engine manufacturers to push the limits of technology.

其一是昂贵的油价和航空公司间残酷的竞争，在飞机和引擎制造商上施加比以往更大的压力，促使它们跨越技术障碍。

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Recycling second-hand aircraft carrier, overhaul nuclear reactor, unpick and wash missile engine oil, clean aircraft carrier, space shuttle, maintenance, such change.

回收二手航母，大修核反应堆，拆洗和洗导弹发动机油，清洁的航空母舰，航天飞机，维修，这样的变化。

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But the shift towards synthetic fuel has provoked criticism, because when such fuel is made from coal and then burned in an aircraft engine, more greenhouse gases are emitted overall than would be produced if the aircraft simply burned conventional fuel derived from oil.

ECONOMIST: Monitor