With no road signs and few maps, they had to put their trust in directions passed by word of mouth and in secret signsnails driven into trees, for example-that conductors used to mark the route north.
没有路标，地图也很少，他们只好信赖别人给他们所指路的方向以及自己辨认那些钉在树上的暗号：例如，通常过去的向导都会留下向北的路标暗号。
Sea ice cover is in a downward spiral and may have passed the point of no return, with a possible ice-free Arctic Ocean by summer 2030, senior scientist Mark Serreze said.
资深科学家马克?塞雷利兹说，北极海冰面积呈螺旋式下降而且可能已经超过极限点。到2030年夏季，北冰洋的海冰可能将全部融化。
Sea ice cover is in a downward spiral and may have passed the point of no return, with a possible ice-free Arctic Ocean by summer 2030, senior scientist Mark Serreze said.
资深科学家马克?塞雷利兹说，北极海冰面积呈螺旋式下降而且可能已经超过极限点。到2030年夏季，北冰洋的海冰可能将全部融化。
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