Progress in the development of renewables could be fragile, however, if fossil fuel prices remain low for long.
然而，如果化石燃料价格长期保持低位，可再生能源的发展进程可能会非常脆弱。
2
Many species appear to remain unchanged in the fossil record for millions of years—a situation that seems to be at odds with Darwin's model of continuous change.
许多物种似乎在数百万年的化石记录中都保持不变——而这种情况似乎与达尔文的持续变化模型不一致。
3
The report said that fossil fuels — especially from the major oil-exporting nations in the Mideast — will remain as the world's main energy source.